feat(model): add alert Block Kit block

[zimeg]

Summary

Adds the alert Block Kit layout block to slack-api-model, following the existing HeaderBlock / MarkdownBlock conventions (Lombok @Data @Builder @NoArgsConstructor @AllArgsConstructor, TYPE constant, javadoc docs link).

The alert block displays an inline alert message and is currently only supported in modals.

Fields

• text — plain_text or mrkdwn text object (modeled as TextObject), max 200 characters. Required.
• level — severity: default | info | warning | error | success. Defaults to default when omitted.
• block_id — optional unique identifier.

Changes

• New AlertBlock model class.
• Registered alert type in GsonLayoutBlockFactory.
• Added alert(...) DSL helper to Blocks.
• Added parseAlertBlocks (deserialization) and buildAlertBlock (builder + serialize round-trip) tests in BlockKitTest.

Docs reference

https://docs.slack.dev/reference/block-kit/blocks/alert-block

Validation

Ran the touched module's tests:

./mvnw -pl slack-api-model test -Dtest=BlockKitTest -Djacoco.skip=true

Result: PASS — Tests run: 45, Failures: 0, Errors: 0, Skipped: 0 (includes the two new alert tests).

Note: JaCoCo coverage instrumentation had to be skipped because the repo's pinned JaCoCo version cannot instrument Java 25 (Unsupported class file major version 69) class files in this environment; this is a local toolchain limitation unrelated to this change. The unit tests themselves pass.

Co-Authored-By: Claude svc-devxp-claude@slack-corp.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.33%. Comparing base (a312395) to head (8259f2d).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1610   +/-   ##
=========================================
  Coverage     73.32%   73.33%           
- Complexity     4520     4522    +2     
=========================================
  Files           478      478           
  Lines         14300    14302    +2     
  Branches       1490     1490           
=========================================
+ Hits          10486    10488    +2     
  Misses         2923     2923           
  Partials        891      891           

Flag	Coverage Δ
jdk-14	73.33% <100.00%> (+<0.01%)	⬆️

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