feat(storage): add support for bucket metadata call in async client

[bajajneha27]

No description provided.

[gemini-code-assist]

Code Review

This pull request implements the asynchronous GetBucket API across the Google Cloud Storage C++ SDK, including client interfaces, connection implementations, decorators, stubs, mocks, and tests. A review of the changes identified an issue in the integration tests where BucketName is constructed with an already-prefixed string, which would result in a double-prefixed bucket name.

[gemini-code-assist]

The BucketName constructor expects the simple bucket name (e.g., my-bucket), and its FullName() method automatically prepends the projects/_/buckets/ prefix. Passing a string that already contains the prefix will result in a double-prefixed name like projects/_/buckets/projects/_/buckets/.... You should pass only the random name to BucketName.

          .GetBucket(BucketName(MakeRandomObjectName()))

[codecov]

Codecov Report

❌ Patch coverage is 87.14286% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.26%. Comparing base (40d3ab0) to head (0f51cbd).

Files with missing lines	Patch %	Lines
...gle/cloud/storage/internal/storage_tracing_stub.cc	0.00%	7 Missing ⚠️
...cloud/storage/internal/async/connection_tracing.cc	0.00%	5 Missing ⚠️
.../storage/internal/storage_round_robin_decorator.cc	0.00%	3 Missing ⚠️
google/cloud/storage/async/idempotency_policy.cc	50.00%	2 Missing ⚠️
google/cloud/storage/async/client_test.cc	98.14%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16262      +/-   ##
==========================================
- Coverage   92.27%   92.26%   -0.01%     
==========================================
  Files        2214     2214              
  Lines      206505   206645     +140     
==========================================
+ Hits       190549   190669     +120     
- Misses      15956    15976      +20     

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