Enable FA (future annotations) linting ruleset

[pakagronglb]

We already use future annotations (from __future__ import annotations) in most of the codebase. This change enables the FA linting ruleset to ensure consistent usage across all files by:

1. Removing "FA" from the ruleset ignore list in pyproject.toml
2. Running linter checks with tox -e lint to verify compliance
3. Running full test suite with tox to ensure no regressions

The linter passes without any FA-related issues, confirming that our codebase already follows the future annotations best practices consistently.

Testing:

• ✓ Ran tox -e lint - all checks passed
• ✓ Ran full test suite with tox - all tests passed

[jku]

Looks good.

• This project requires a signed-off-by line in the commit message (sorry, CNCF requires that): feel free to do a git commit --amend --signoff and a force push. More info.
• left a question about a docstring change

[jku]

LGTM, thanks for the contribution!