impl(bigquery): add attach_job method to query client

[haphungw]

Add BigQuery::attach_job to bind an existing out-of-process query job reference (JobReference) to a high-level Query handle without re-submitting SQL.

[gemini-code-assist]

Code Review

This pull request introduces the ability to configure a default Google Cloud project ID on the BigQuery client and adds an attach_job method to bind existing out-of-process query jobs. The feedback recommends refactoring the nested if-else block in attach_job using Rust's let-else syntax to reduce indentation, and replacing .unwrap() calls with .expect() in the new unit tests to adhere to the repository's style guide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.27%. Comparing base (e71018a) to head (30216c5).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6295   +/-   ##
=======================================
  Coverage   96.26%   96.27%           
=======================================
  Files         283      283           
  Lines       73009    73096   +87     
=======================================
+ Hits        70279    70370   +91     
+ Misses       2730     2726    -4     

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[suzmue]

I’m a little unsure about InvalidJobReference(String) here. Since the only validation failure we currently handle is a missing job_id, it feels more consistent with MissingProjectId to add a specific MissingJobId variant instead of a more generic error. Are there other errors that we are expecting will be encapsulated by this type?

[alvarowolfx]

I'm not sure if we should introduce another branch for missing information for Job. Maybe we should bundle MissingProjectId and InvalidJobReference into a BindingError ? I think that's how it's done in other veneers. Will check here and come back to that.

[haphungw]

@suzmue @alvarowolfx
I agree we should consolidate these.

I checked gaxi BindingError, but it seems to be a group of REST URL routing failures (like PathMismatch). It would be pretty awkward to construct for simple manual struct validation here.

To keep things clean, I merged MissingProjectId and InvalidJobReference into QueryError::InvalidArgument(String). This covers both missing project and job IDs (and potential future errors) without cluttering the enum.

[dbolduc]

(drive by)

I checked gaxi BindingError, but it seems to be a group of REST URL routing failures (like PathMismatch).

True. Calling it Path was probably a failure to generalize from me.

It would be pretty awkward to construct for simple manual struct validation here.

It's bad but not sooo bad: https://github.com/googleapis/google-cloud-rust/pull/6253/changes