Modernize Python typing across the codebase

Automated via ruff UP006, UP007, UP035, UP045 rules (target: py311):

- Replace `typing.List`, `Dict`, `Tuple`, `Set`, `FrozenSet`, `Type`
  with their built-in equivalents (`list`, `dict`, `tuple`, etc.)
- Replace `typing.Optional[X]` with `X | None`
- Replace `typing.Union[X, Y]` with `X | Y`
- Move `Mapping`, `Sequence`, `Callable`, `Awaitable`,
  `MutableMapping`, `MutableSequence`, `Iterator`, `AsyncIterator`,
  `AsyncGenerator` imports from `typing` to `collections.abc`
- Remove now-unused `typing` imports
- Add `from __future__ import annotations` to 5 files that use
  forward-reference strings in `X | "Y"` annotations

examples/turn-management/turn-management-user-assistant-turns.py

@@ -45,13 +45,13 @@ class TranscriptHandler:
         output_file: Optional path to file where transcript is saved. If None, outputs to log only.
     """
 
-    def __init__(self, output_file: Optional[str] = None):
+    def __init__(self, output_file: str | None = None):
         """Initialize handler with optional file output.
 
         Args:
             output_file: Path to output file. If None, outputs to log only.
         """
-        self.output_file: Optional[str] = output_file
+        self.output_file: str | None = output_file
         logger.debug(
             f"TranscriptHandler initialized {'with output_file=' + output_file if output_file else 'with log output only'}"
         )