impl(bigquery): add query polling and complete query

[alvarowolfx]

Towards #5844

[gemini-code-assist]

Code Review

This pull request implements query polling capabilities in the BigQuery crate, introducing the Query::until_done method, a CompleteQuery handle, and a poll_query_results helper function that uses exponential backoff. It also adds comprehensive unit tests to verify these behaviors. The review feedback points out violations of the repository style guide regarding the use of unwrap() and expect() in production code within the polling helper, recommending proper error propagation instead.

[gemini-code-assist]

According to the Repository Style Guide, unwrap() should not be used in production code. Instead of panicking on failure, handle the error by mapping it to a QueryError and propagating it using the ? operator.

    let backoff_policy = ExponentialBackoffBuilder::default()
        .with_maximum_delay(std::time::Duration::from_secs(10))
        .build()
        .map_err(|e| {
            QueryError::Rpc {
                source: google_cloud_gax::error::Error::service(
                    google_cloud_gax::error::rpc::Status::default()
                        .set_code(google_cloud_gax::error::rpc::Code::Internal)
                        .set_message(format!("failed to build backoff policy: {e}")),
                ),
            }
        })?;

References

1. No unwrap() or expect() in production code or examples (use ? or handle errors). ^(link)

[gemini-code-assist]

According to the Repository Style Guide, expect() should not be used in production code. Instead of panicking if the job reference is missing, return a QueryError explicitly.

Suggested change

	let job_ref = job_ref.expect("query job should have job reference at this point");
	let job_ref = job_ref.ok_or_else(|| {
	QueryError::Rpc {
	source: google_cloud_gax::error::Error::service(
	google_cloud_gax::error::rpc::Status::default()
	.set_code(google_cloud_gax::error::rpc::Code::InvalidArgument)
	.set_message("query job should have job reference at this point"),
	),
	}
	})?;

References

1. No unwrap() or expect() in production code or examples (use ? or handle errors). ^(link)

[codecov]

Codecov Report

❌ Patch coverage is 99.13043% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.90%. Comparing base (d059878) to head (b49514e).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bigquery/src/query/query_handle.rs	99.11%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #5896    +/-   ##
========================================
  Coverage   97.89%   97.90%            
========================================
  Files         233      234     +1     
  Lines       59202    59432   +230     
========================================
+ Hits        57958    58189   +231     
+ Misses       1244     1243     -1     

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