Add type annotations for core utility modules

[Erotemic]

Motivation

• Improve static typing coverage across core utility modules to enable stricter mypy checking.
• Make public and internal APIs explicitly typed while preserving existing runtime behavior.
• Reduce reliance on untyped or loosely-typed signatures to surface clearer contracts for callers and maintainers.

Description

• Annotated OrderedSet with generics (TypeVar), precise container types, overloads for __getitem__, and targeted cast usage to satisfy Sequence/MutableSet expectations.
• Added explicit parameter and return type annotations to CLI helpers argval and argflag using Union/Optional types.
• Typed color/highlight utilities in util_colors.py by annotating highlight_code, _pygments_highlight, _rich_highlight, and color_text and adding Any for flexible kwargs.
• Tightened typing for the NoParam sentinel and schedule_deprecation in util_const.py and util_deprecate.py by adding return/type annotations, cast usage, and handling packaging.version.Version correctly.

Testing

• Ran mypy ubelt/orderedset.py ubelt/util_arg.py ubelt/util_colors.py ubelt/util_const.py ubelt/util_deprecate.py and observed Success: no issues found.
• Ran the full test suite with python run_tests.py and observed 580 passed, 28 skipped.

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Codex Task