fix: Support Field defined via typing_extensions.Annotated

[MarshalX]

For reviewers

• I did not use AI
• I used AI and thoroughly reviewed every code/docs change

Description of the change

#46 checks canonical_path == "typing.Annotated", so typing_extensions.Annotated[int, Field(description="...", le=10)] never enters that branch. The description and constraints are dropped.

Now matches typing_extensions.Annotated too. New test mirrors test_annotated_fields with typing_extensions, and also asserts that a constraint declared inside Annotated is collected.

Relevant resources

• Introduced in feat: Supports Pydantic Field defined via Annotated #46
• Original request: bug: Annotated causes fields to not show up with description #37

[pawamoy]

Looks like a no-brainer, thanks 🙂