Revert union type syntax from | to Union[] for Python 3.9 runtime compatibility

[Copilot]

What does this changes

Replaces all A | B union type syntax with Union[A, B] and Optional[A] in type hints across 8 files in corpus, tools, util, and tag modules.

What was wrong

The | union syntax fails at runtime in Python 3.9 when introspection tools call typing.get_type_hints(), despite from __future__ import annotations allowing it to parse. This breaks static analysis tools, documentation generators, and runtime type inspection.

# Before: Parses but breaks get_type_hints() in Python 3.9
def provinces(details: bool = False) -> frozenset[str] | list[dict[str, str]]:
    ...

# After: Works with runtime introspection
def provinces(details: bool = False) -> Union[frozenset[str], list[dict[str, str]]]:
    ...

How this fixes it

• corpus/common.py: Union[frozenset[str], list[dict[str, str]]]
• corpus/core.py: Optional[_ResponseWrapper]
• tools/misspell.py: Optional[tuple[...]], Optional[list[str]]
• util/date.py: Optional[int]
• util/keyboard.py: Optional[list[list[str]]]
• util/wordtonum.py: tuple[bool, Optional[str]]
• tag/wangchanberta_onnx.py: Union[str, list[tuple[str, str]]]
• tag/crfchunk.py: Union[str, bool], Optional[type[BaseException]], Optional[types.TracebackType]

Added necessary Union and Optional imports where missing.

Your checklist for this pull request

• Passed code styles and structures
• Passed code linting checks and unit test

Original prompt

Find in the code, code comments, and documentation for wrong type hints or inconsistent type hints.

Fix them. Start with pythainlp.tokenize, pythainlp.corpus, pythainlp.util, pythainlp.tools, and pythainlp.tag.
Keep the Python 3.9 compatibility (with import future annotations).

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[coveralls]

coverage: 53.644% (+0.03%) from 53.614%
when pulling b373acc on copilot/fix-type-hints-inconsistencies
into e4c6f6b on dev.

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud