feat(core): add KeyAuth.close() to stop the token refresh thread

[mittalpk]

Description

relates to #10253

KeyAuth started a daemon refresh thread that looped forever with no way to stop it, so every discarded instance (for example after key rotation in a long-running process) kept a thread alive that kept requesting tokens. This adds a public, idempotent close(), as proposed in the issue: the loop now waits on a stop event, and close() sets it, shuts down the refresh executor, unregisters the atexit hook and joins the thread.

I bumped core to v0.4.0 since this adds a public method. v0.3.1 is not released yet, so I'm happy to fold this into it if you prefer.

Checklist

• Issue was linked above
• No generated code was adjusted manually (check comments in file header)
• Changelogs and versioning
  • Changelog in root directory was adjusted (see here)
  • Changelog of the service(s) was adjusted (see e.g. here)
  • pyproject.toml of the service(s) was adjusted (see e.g. here)
• Examples were added / adjusted (see examples/ directory)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)

[cgoetz-inovex]

Hi @mittalpk,
thanks for your contribution, CI is currently failing with:

Lock file for alb is out of date. Run 'make update-dependencies'.

[mittalpk]

Thanks, the core version bump left the service lock files stale. I ran make update-dependencies and pushed the relocked files.