Enforce strict type checking and remove suppressions

[BeathovenGala]

Issue

Enable strict type checking and resolve pytype workarounds #206

Description:

This PR enforces strict type checking by removing the lenient configuration and cleaning up explicit suppressions in the codebase.

Changes:

1. Strict Configuration:

   • Updated pyproject.toml to remove keep_going = true. This ensures pytype fails immediately on errors, enforcing a "zero tolerance" policy for new type violations.

2. Engine Interface Fix:

   • Widened the return type of Engine.next_acting in concordia/environment/engine.py to correctly support parallel engines that return lists of entities instead of just single tuples.
   • Old signature: tuple[Entity, ActionSpec]
   • New signature: tuple[...] | Sequence[Entity] | tuple[Sequence[Entity], ...]

3. Removed Suppressions:

   • Removed pytype: disable=signature-mismatch from 3 engine implementations (parallel_questionnaire.py, sequential_questionnaire.py, simultaneous.py) as they now comply with the widened base class interface.
   • Removed pytype: disable=override-error from entity_agent.py and simple_llm_agent.py.

Verification:

Ran full test suite (pytest --pyargs concordia). All tests passed,(Will work with the tempory fix from #211 or in some time ) confirming that the interface widening did not introduce runtime regressions.