feat: add ASOF joins to DataFrame API

[Xuanwo]

Which issue does this PR close?

• Part of ASOF join support / Specialize Range Joins #318.
• Umbrella PR: feat: support ASOF joins #23738.
• Depends on feat: add ASOF join logical semantics #23829 (and transitively feat: add ASOF join physical operator #23828, which is merged).

Rationale for this change

This is the DataFrame API layer of the ASOF JOIN stack. It exposes the logical
contract through the fluent API without coupling that API review to SQL parsing
or protobuf changes.

GitHub shows the cumulative stack because fork branches cannot be selected as
upstream PR bases. The isolated diff for this layer is:
Xuanwo/datafusion@xuanwo/asof-logical...xuanwo/asof-dataframe

What changes are included in this PR?

• Add DataFrame::join_asof for expression-based equality keys.
• Add DataFrame::join_asof_using for same-named equality keys.
• Export AsOfMatch and Operator from the DataFusion prelude.
• Add a DataFrame-only execution test that exercises the broadcast physical
  operator without depending on SQL syntax.

Are these changes tested?

Yes:

• cargo fmt --all
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test -p datafusion --test core_integration dataframe::join_asof --all-features
• The extended workspace test command from the contributor guide

Are there any user-facing changes?

Users can build ASOF joins through DataFrame::join_asof and
DataFrame::join_asof_using. The USING form follows DataFusion's existing
name-resolution contract: wildcard output exposes one unqualified key while
both qualified input keys remain addressable.

This PR should be reviewed and merged after #23829. It does not depend on the
optional floating-point follow-up #24375.

[github-actions]

Thank you for opening this pull request!

Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch).

Details

     Cloning apache/main
    Building datafusion v55.0.0 (current)
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    Checking datafusion v55.0.0 -> v55.0.0 (no change; assume patch)
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     Summary no semver update required
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    Checking datafusion-expr v55.0.0 -> v55.0.0 (no change; assume patch)
     Checked [   1.487s] 223 checks: 222 pass, 1 fail, 0 warn, 31 skip

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/enum_variant_added.ron

Failed in:
  variant LogicalPlan:AsOfJoin in /home/runner/work/datafusion/datafusion/datafusion/expr/src/logical_plan/plan.rs:301
  variant LogicalPlan:AsOfJoin in /home/runner/work/datafusion/datafusion/datafusion/expr/src/logical_plan/plan.rs:301

     Summary semver requires new major version: 1 major and 0 minor checks failed
    Finished [  49.365s] datafusion-expr
    Building datafusion-optimizer v55.0.0 (current)
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    Building datafusion-optimizer v55.0.0 (baseline)
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      Parsed [   0.027s] (baseline)
    Checking datafusion-optimizer v55.0.0 -> v55.0.0 (no change; assume patch)
     Checked [   0.182s] 223 checks: 223 pass, 31 skip
     Summary no semver update required
    Finished [  44.571s] datafusion-optimizer
    Building datafusion-physical-plan v55.0.0 (current)
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     Summary no semver update required
    Finished [  63.151s] datafusion-physical-plan
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     Parsing datafusion-proto v55.0.0 (baseline)
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     Summary no semver update required
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    Building datafusion-sql v55.0.0 (baseline)
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     Parsing datafusion-sql v55.0.0 (baseline)
      Parsed [   0.029s] (baseline)
    Checking datafusion-sql v55.0.0 -> v55.0.0 (no change; assume patch)
     Checked [   0.261s] 223 checks: 223 pass, 31 skip
     Summary no semver update required
    Finished [  68.537s] datafusion-sql
    Building datafusion-substrait v55.0.0 (current)
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     Parsing datafusion-substrait v55.0.0 (current)
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    Building datafusion-substrait v55.0.0 (baseline)
       Built [ 247.288s] (baseline)
     Parsing datafusion-substrait v55.0.0 (baseline)
      Parsed [   0.015s] (baseline)
    Checking datafusion-substrait v55.0.0 -> v55.0.0 (no change; assume patch)
     Checked [   0.249s] 223 checks: 223 pass, 31 skip
     Summary no semver update required
    Finished [ 495.807s] datafusion-substrait

[codecov-commenter]

Codecov Report

❌ Patch coverage is 61.12469% with 159 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.52%. Comparing base (c4910e0) to head (f2bcdf6).
⚠️ Report is 20 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/expr/src/logical_plan/plan.rs	50.76%	81 Missing and 15 partials ⚠️
datafusion/expr/src/logical_plan/builder.rs	60.71%	17 Missing and 5 partials ⚠️
datafusion/core/src/dataframe/mod.rs	43.33%	15 Missing and 2 partials ⚠️
datafusion/expr/src/logical_plan/display.rs	0.00%	10 Missing ⚠️
datafusion/core/src/physical_planner.rs	82.92%	5 Missing and 2 partials ⚠️
datafusion/expr/src/logical_plan/tree_node.rs	93.02%	0 Missing and 3 partials ⚠️
datafusion/optimizer/src/analyzer/type_coercion.rs	92.85%	1 Missing and 1 partial ⚠️
datafusion/optimizer/src/optimizer.rs	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23831      +/-   ##
==========================================
+ Coverage   81.47%   81.52%   +0.04%     
==========================================
  Files        1122     1123       +1     
  Lines      403629   406508    +2879     
  Branches   403629   406508    +2879     
==========================================
+ Hits       328866   331387    +2521     
- Misses      55510    55725     +215     
- Partials    19253    19396     +143     

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