jwtauthccl: JWT token Authentication kills SQL session on token expiry

**Is your feature request related to a problem? Please describe.**
We believe that the SQL session will remain open, even after the JWT token has expired.

**Describe the solution you'd like**
CockroachDB reads the JWT token expiry from the token, realises the JWT token will expire at X time and kills the session on expiry.

**Describe alternatives you've considered**
Killing sessions manually.

**Additional context**
Add any other context or screenshots about the feature request here.

Jira issue: CRDB-28656

Epic CRDB-54682

No files, tests, or entry points are identified. Start by tracing the jwtauthccl authentication path and the SQL session lifecycle, then clarify whether an expired JWT should keep the session open or terminate it. Done should include agreed expiry behavior and coverage for the token-expiry case.

Written by the indexing model from the issue text.