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

tests/test_vad_processor.py

@@ -5,7 +5,6 @@
 #
 
 import unittest
-from typing import List
 
 from pipecat.audio.vad.vad_analyzer import VADAnalyzer, VADState
 from pipecat.frames.frames import (
@@ -22,7 +21,7 @@ from pipecat.tests.utils import run_test
 class MockVADAnalyzer(VADAnalyzer):
     """A mock VAD analyzer that returns states from a predefined sequence."""
 
-    def __init__(self, states: List[VADState]):
+    def __init__(self, states: list[VADState]):
         super().__init__(sample_rate=16000)
         self._states = list(states)
         self._call_index = 0