fix: resolve CI failures, drop Python 3.9, and clean up test deprecations

[aseering]

This PR addresses several underlying issues causing CI flakiness and hard failures, alongside general code health improvements to clean up the test
output.

Changes Made:

• Fix Spanner Metrics Exporter Crash (fix)

  • Issue: The OpenTelemetry background thread was attempting to export project-level metrics using the spanner_instance_client resource type,
    which requires an instance_id. Missing labels caused 400 InvalidArgument errors, crashing the thread and failing the Nox session.
  • Fix: Updates CloudMonitoringMetricsExporter to inject project_id and silently drop metrics lacking an instance_id.

• Drop Python 3.9 Support (build)

  • Issue: Kokoro environment issues with unit-3.9 and outdated infrastructure.
  • Fix: Performed a comprehensive removal of Python 3.9 support across noxfile.py, setup.py, .kokoro/ configurations, .librarian/ (synthtool
    inputs), and GitHub Actions.

• Fix SyntaxWarning in cursor.py (fix)

  • Issue: Python 3.14 emits a warning for return inside a finally block as it swallows exceptions.
  • Fix: Moved return rows out of the finally block in google/cloud/spanner_dbapi/cursor.py.

• Resolve Deprecation Warnings & Pytest Issues (chore)

  • Issue: Deprecated datetime.utcnow() and pytest collection warnings for classes starting with Test.
  • Fix: Migrated to timezone-aware datetime.now(timezone.utc) and renamed TestCredentials to MockCredentials.

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the stability and maintainability of the codebase by addressing critical CI failures and cleaning up test output. It resolves a metrics exporter crash, removes support for an outdated Python version, fixes a SyntaxWarning, and updates deprecated datetime usage and pytest class naming conventions. The overall impact is a more robust and less noisy development and testing environment.

Highlights

• Spanner Metrics Exporter Crash Fixed: Resolved an issue where the OpenTelemetry background thread crashed due to invalid metrics lacking 'instance_id', by ensuring 'project_id' injection and silently dropping problematic metrics.
• Python 3.9 Support Dropped: Removed Python 3.9 from CI configurations and noxfile.py due to environment support issues, streamlining the build process.
• SyntaxWarning in cursor.py Resolved: Addressed a Python 3.14 SyntaxWarning by moving the 'return rows' statement out of a 'finally' block in google/cloud/spanner_dbapi/cursor.py.
• Deprecation Warnings & Pytest Issues Cleaned Up: Migrated 'datetime.utcnow()' to timezone-aware 'datetime.now(timezone.utc)' and renamed 'TestCredentials' to 'MockCredentials' to eliminate test log noise and pytest collection warnings.

Changelog

• google/cloud/spanner_dbapi/cursor.py
  • Moved 'return rows' statement outside the 'finally' block to prevent SyntaxWarning.
• google/cloud/spanner_v1/metrics/metrics_exporter.py
  • Converted a static method to an instance method.
  • Injected 'project_id' into monitored resource labels.
  • Added logic to filter out metrics missing 'instance_id' to prevent exporter crashes.
• google/cloud/spanner_v1/pool.py
  • Updated the '_NOW' function to use 'datetime.now(datetime.timezone.utc)' instead of 'datetime.utcnow'.
• google/cloud/spanner_v1/session.py
  • Imported 'timezone' from 'datetime'.
  • Updated '_last_use_time' initialization to use 'datetime.now(timezone.utc)'.
• tests/system/test_dbapi.py
  • Replaced 'datetime.datetime.utcnow().replace(tzinfo=UTC)' with 'datetime.datetime.now(UTC)'.
• tests/system/test_session_api.py
  • Replaced 'datetime.datetime.utcnow().replace(tzinfo=UTC)' with 'datetime.datetime.now(UTC)' in multiple test cases.
• tests/unit/test__helpers.py
  • Renamed the internal test class 'test_class' to 'MockClass' and updated all references to it.
• tests/unit/test_backup.py
  • Updated timestamp creation to use 'datetime.datetime.now(UTC)' and 'datetime.now(timezone.utc)'.
• tests/unit/test_batch.py
  • Replaced 'datetime.datetime.utcnow().replace(tzinfo=UTC)' with 'datetime.datetime.now(UTC)' in several commit-related tests.
• tests/unit/test_database.py
  • Updated timestamp creation to use 'datetime.datetime.now(UTC)' in various test methods.
• tests/unit/test_instance.py
  • Updated timestamp creation to use 'datetime.datetime.now(UTC)'.
• tests/unit/test_metrics.py
  • Renamed 'TestCredentials' to 'MockCredentials'.
  • Updated client initialization to use 'MockCredentials'.
  • Added 'patch' context managers for metric service client and exporter.
• tests/unit/test_pool.py
  • Imported 'timezone' from 'datetime'.
  • Updated 'datetime.utcnow()' calls to 'datetime.now(timezone.utc)' or 'datetime.now(UTC)' in session pool tests.
• tests/unit/test_session.py
  • Replaced 'datetime.datetime.utcnow().replace(tzinfo=UTC)' with 'datetime.datetime.now(UTC)' in numerous transaction-related tests.

Activity

• No specific human activity (comments, reviews, progress updates) has been recorded for this pull request.

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[gemini-code-assist]

Code Review

This pull request introduces a set of valuable changes that address CI failures, remove support for Python 3.9, and clean up various deprecation warnings in the test suite. The fix for the Spanner Metrics Exporter crash, by ensuring project_id is present and filtering out metrics lacking an instance_id, is well-implemented and correctly addresses the underlying issue. The codebase is also improved by replacing deprecated datetime.utcnow() calls with the timezone-aware datetime.now(timezone.utc) and resolving a SyntaxWarning in cursor.py. The test suite is made more robust by renaming helper classes to avoid pytest warnings. Overall, the changes are correct and improve the health and reliability of the codebase.