test(spanner): support running integration tests on real Spanner

[olavloite]

The Spanner integration tests are executed against the Spanner emulator in the CI
builds, as the emulator is significantly faster for typical test workloads, such
as repeatedly executing DDL statements. This change adds support for running the
same integration tests against a real Spanner instance.

[gemini-code-assist]

Code Review

This pull request enables integration tests to run against real Google Cloud Spanner instances in addition to the emulator. It introduces a define_test_suites! macro in the test driver to manage the lifecycle of tests, including client provisioning and shared database cleanup. Key changes include the addition of google-cloud-spanner-admin-database-v1 for database management, logic to clean up stale test databases, and updates to existing tests to handle behavioral differences between the emulator and real Spanner, such as varying error types and query statistics. I have no feedback to provide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.89%. Comparing base (eeb17aa) to head (6fb0485).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5683   +/-   ##
=======================================
  Coverage   97.89%   97.89%           
=======================================
  Files         226      226           
  Lines       55405    55405           
=======================================
  Hits        54236    54236           
  Misses       1169     1169           

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