fix(typing): runtime NameError in DictBasedTypingSystem.construct_state, correct ActionSchema abstract signatures

[adawang1210]

Summary

DictBasedTypingSystem.construct_state() crashed with NameError: name 'State' is not defined whenever it was actually called -- State is only imported under TYPE_CHECKING in burr/core/typing.py. This is reachable from the public API: ApplicationBuilder.with_state(<non-State object>) with a dict-based typing system hits this path (application.py calls self.typing_system.construct_state(state)). Additionally, ActionSchema's abstract methods were declared without self, contradicting every concrete implementation (DefaultSchema, the pydantic integration), and an unused Self import fallback was dead code.

Changes made

• burr/core/typing.py:
  • construct_state now imports State locally at runtime (module-level would be circular -- state.py imports from typing.py), fixing the NameError.
  • ActionSchema.state_input_type / state_output_type / intermediate_result_type abstract declarations now take self, matching all implementations.
  • Removed the unused try: from typing import Self fallback (never referenced).
• tests/core/test_typing.py (new): covers DictBasedTypingSystem behavior including the previously-crashing construct_state, a conforming ActionSchema subclass, ABC enforcement for incomplete subclasses, and DEFAULT_SCHEMA semantics.

How to test

pytest tests/core/test_typing.py

Repro of the bug on main:

from burr.core.typing import DictBasedTypingSystem
DictBasedTypingSystem().construct_state({"a": 1})  # NameError before this fix

Checklist

• Tests added or updated
• All tests pass locally (pytest tests/ --ignore=tests/integration_tests: 577 passed, 5 skipped)
• Commits signed off (git commit -s)
• Pre-commit hooks pass (black, isort, flake8)
• CONTRIBUTING.md guidelines followed

[github-actions]

This PR has had no activity for 95 days.
Closing to keep the PR list manageable.

Feel free to reopen when you are ready to continue.
If the branch has conflicts, a fresh PR against main might be easier.