docs(bigquery): improve Query handles docs

[alvarowolfx]

Towards #5844

[gemini-code-assist]

Code Review

This pull request adds comprehensive documentation and usage examples to the Query, CompleteQuery, and RunQuery structs in the BigQuery query module. The feedback points out incorrect import paths for QueryReference in the newly added documentation and examples, which would cause broken intra-doc links and rustdoc warnings.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.26%. Comparing base (4ff2683) to head (1de1692).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6212   +/-   ##
=======================================
  Coverage   96.26%   96.26%           
=======================================
  Files         282      282           
  Lines       73304    73304           
=======================================
+ Hits        70563    70567    +4     
+ Misses       2741     2737    -4     

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[alvarowolfx]

/gemini review

[gemini-code-assist]

Code Review

This pull request significantly improves the documentation for the BigQuery query execution API by adding comprehensive doc comments, usage examples, and error explanations for the Query, CompleteQuery, and RunQuery structs and their associated methods. I have no feedback to provide as there are no review comments.