ci: add Python compatibility checks

[lmatz]

Summary

• add a GitHub Actions workflow to compile and import the server on multiple Python versions
• cover Python 3.8, 3.11, 3.12, and 3.13 explicitly
• make future syntax-compat regressions fail in CI instead of at user startup time

Validation

• workflow reviewed locally for syntax
• bug-fix branch below already validated on 3.8/3.11/3.12/3.13
• this PR is stacked on fix: restore Python 3.8-3.11 compatibility in iceberg SQL builders #16 so CI runs against the fixed source tree

Stacked on

• fix: restore Python 3.8-3.11 compatibility in iceberg SQL builders #16