Fix TypeError in type_info for mixed-type Literals

[lawrence3699]

Closes #1018

inspect.type_info() crashes with TypeError when called on Literal types that mix value types:

import msgspec.inspect as mi
from typing import Literal

mi.type_info(Literal[1, None])
# TypeError: '<' not supported between instances of 'NoneType' and 'int'

Cause: sorted(args) on line 888 fails in Python 3 when args contain values of different types (e.g. int and NoneType).

Fix: Use a type-aware sort key ("", 0) if x is None else (type(x).__name__, x) that groups values by type name, with None always sorting first. Also updates the LiteralType.values annotation to Tuple[Union[None, int, str], ...] since mixed-type tuples are valid.

Before: type_info(Literal[1, None]) raises TypeError
After: type_info(Literal[1, None]) returns LiteralType(values=(None, 1))

Existing behavior for same-type Literals is unchanged (e.g. Literal[3, 1, 2] still produces (1, 2, 3)).

Validation: all 168 inspect tests pass (including 4 new regression tests), ruff lint + format clean.

[Copilot]

Pull request overview

Fixes a TypeError in msgspec.inspect.type_info() when inspecting typing.Literal types containing mixed value types (e.g., Literal[1, None]) by introducing a type-aware sort, and expands LiteralType.values typing/docs to cover mixed literal value tuples.

Changes:

• Replace sorted(args) for Literal[...] handling with a type-aware sort key to avoid cross-type comparison errors.
• Widen LiteralType.values annotation and update its docstring to reflect supported mixed literal values.
• Add regression tests covering None and mixed (None, int, str) literal combinations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/msgspec/inspect.py	Makes Literal[...] translation robust to mixed-type literal args and updates LiteralType.values typing/docs.
tests/unit/test_inspect.py	Adds regression tests validating type_info() output ordering for mixed-type Literal values.

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[Copilot]

type_info() now returns mixed-type LiteralType.values by using a custom sort key, but msgspec.json.schema still does sorted(t.values) (see src/msgspec/_json_schema.py:367), which will continue to raise TypeError for mixed (None, int, str) enums. Consider either relying on the already-normalized ordering from type_info (no downstream re-sort), or factoring this sort key into a shared helper and reusing it in schema generation too.

[Siyet]

Tested on a Linux VPS (Python 3.12, Ubuntu): all 168 inspect tests green, including the 4 new ones. Also ran 12 extra edge-case scenarios (negative ints, single-element Literals, multi-type mixes), all pass.

Two things to address:

1. +1 to Copilot's inline: confirmed on VPS that msgspec.json.schema(Literal[1, None]) crashes with TypeError.
2. Sort order (None first, then by type name, then by value) is not documented. A comment on the lambda would help.