impl(bigquery): dry run queries should be routed to jobs.insert

[alvarowolfx]

jobs.query don't provide full job statistics, so routing to jobs.insert is more useful. Also, since dry run queries don't have queries results or are marked as complete, we change examples to show just using a Query handle, not until_done or a CompleteQuery. Right now calling until_done it's going to throw a RPC Binding Error (empty job_id), but will eval if worth it introducing a new QueryError::DryRunQuery

Supersedes #6508

[gemini-code-assist]

Code Review

This pull request updates the BigQuery query execution logic to route dry run queries through the jobs.insert API instead of jobs.query so that full statistics are returned. It also updates the dry run example and adds corresponding unit tests. Feedback was provided regarding a potential panic or RPC error when calling .until_done() on a dry run query, as the returned Job resource may lack a valid active job status or job ID. It is suggested to update Query::from_job to handle dry run queries gracefully by marking them as completed immediately.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.39%. Comparing base (ceb8e53) to head (c254eac).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6523      +/-   ##
==========================================
- Coverage   96.39%   96.39%   -0.01%     
==========================================
  Files         301      301              
  Lines       84762    84808      +46     
==========================================
+ Hits        81709    81752      +43     
- Misses       3053     3056       +3     

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