Adopt PEP 585 / PEP 604 type hints (`list[...]`, `X | None`, `collections.abc`)

[nanotaboada]

Problem

The project targets Python 3.13 (requires-python = ">=3.13.3") but still
imports generic types from typing:

• List[Player], List[PlayerResponseModel]
• Optional[Player], Optional[str]
• Union[UUID, str]
• typing.AsyncIterator, typing.AsyncGenerator

typing.List and friends are documented deprecated aliases; the
typing.AsyncIterator / AsyncGenerator aliases have been soft-deprecated in
favour of collections.abc since 3.9. New code on a modern interpreter should
use the builtin / collections.abc forms.

Proposed Solution

Sweep the annotations. Files affected: main.py, routes/player_route.py,
services/player_service.py, databases/player_database.py,
schemas/player_schema.py, tests/conftest.py.

Before	After
from typing import List / List[X]	list[X]
Optional[X]	X | None
Union[A, B]	A | B
from typing import AsyncIterator	from collections.abc import AsyncIterator
from typing import AsyncGenerator	from collections.abc import AsyncGenerator

Annotated stays imported from typing — it has no builtin equivalent.

Suggested Approach

1. One file at a time: replace the annotations, then prune now-unused typing
   imports.
2. Keep Annotated (and any future TypeVar / Protocol) from typing.
3. Run uv run flake8 and uv run pytest after each file.
4. AsyncGenerator[AsyncSession, None] becomes AsyncGenerator[AsyncSession]
   under collections.abc (the send type defaults to None).

Acceptance Criteria

• No typing.List, typing.Optional, typing.Union remain
• AsyncIterator / AsyncGenerator imported from collections.abc
• Unused typing imports removed
• flake8 clean, all tests pass
• CHANGELOG.md updated

References

• PEP 585 — Type Hinting Generics In Standard Collections
• PEP 604 — Allow writing union types as X | Y
• typing — Deprecated aliases