feat(pubsub): regenerate pubsub library using gapic-generator v1.32.0

[chalmerlowe]

Updates post processing to account for dropping support for Python 3.7, 3.8, 3.9 and impacts that has on using 3.10 for lower bounds testing.

Changes:

• adds grpcio-status, opentelemetry-api, opentelemetry-sdk to constraints-3.10.txt and installs pandas extra in prerelease_deps and core_deps_from_source nox sessions.
• updates dependency versions in constraints-3.10.txt to match expectations in the setup.py file.
• Refined post-processing replacement rules in ``librarian/generator-input/client-post-processing/pubsub-integration.yaml` to make these dependency and constraint alignments.

[gemini-code-assist]

Code Review

This pull request primarily focuses on dropping support for Python 3.9, updating the minimum required version to 3.10, and increasing the lower bounds for dependencies like google-api-core and grpcio-status. It also removes legacy compatibility code for Python versions older than 3.8 and updates test assertions to be order-independent. Reviewer feedback recommends including Python 3.13 in the test matrix and package metadata to ensure consistency with dependency constraints, and suggests restoring the 'warnings as errors' flag for documentation builds to maintain quality.