impl(bigquery): fetch more pages and limit buffered results

[alvarowolfx]

Towards #5844

[gemini-code-assist]

Code Review

This pull request implements pagination support for the BigQuery RowIterator by implementing the fetch_page method using GetQueryResultsRequest, adding a set_max_rows_buffered configuration method, and adding corresponding unit and integration tests. The review feedback suggests avoiding the use of .expect() in fetch_page and instead returning a Result to prevent potential panics, aligning with the repository's style guide.

[gemini-code-assist]

According to the Repository Style Guide (lines 50-59), unwrap() and expect() should typically be avoided in production code, and the library should almost always prefer returning a Result over panicking. Since fetch_page returns a Result, we can safely return a RowError::InvalidRowFormat if job_ref is missing instead of panicking.

Suggested change

	let job_ref = self.job_ref.as_ref().expect(
	"only queries with a job reference should have page tokens and can fetch more pages",
	);
	let job_ref = self.job_ref.as_ref().ok_or_else(|| {
	RowError::InvalidRowFormat("missing job reference for pagination".to_string())
	})?;

References

1. unwrap() and expect() should typically be avoided in production code and examples (use ? or handle errors). The library should almost always prefer to return a Result<> over an internal panic!. ^(link)

[alvarowolfx]

this is an unreachable state. Only happens if the backend runs a query as a stateless job (no job reference) and provide a page token (which is not possible)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.98%. Comparing base (0ea7ea9) to head (511c27f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6032      +/-   ##
==========================================
+ Coverage   96.95%   96.98%   +0.02%     
==========================================
  Files         248      248              
  Lines       62379    62500     +121     
==========================================
+ Hits        60482    60616     +134     
+ Misses       1897     1884      -13     

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