[flake8-pyi] Add "replace with Self" fix (PYI034)

[InSyncWithFoo]

Summary

Resolves #14184.

Test Plan

cargo nextest run and cargo insta test.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[charliermarsh]

Suggested change

	let source_module = if checker.source_type.is_stub() || target_version < (3, 11) {
	"typing_extensions"
	} else {
	"typing"
	let source_module = if checker.source_type.is_stub() || target_version >= (3, 11) {
	"typing"
	} else {
	"typing_extensions"

[charliermarsh]

I think we do want to use typing in stubs.

[InSyncWithFoo]

I don't think Self can be imported from typing on 3.10 and lower, even in stubs. How about if target_version >= (3, 11) { "typing" } else { "typing_extensions" }?

[AlexWaygood]

@InSyncWithFoo is correct -- Self cannot be imported from typing in a .py file or a .pyi file if you want the code to support Python 3.10 or lower (see also: #9761).

In typeshed we always import Self from typing_extensions, because typeshed pretends that typing_extensions is part of the stdlib, and we want our stubs to support Python 3.8-3.13.

[charliermarsh]

Thanks both! I assumed the semantics were similar to PEP 585.

[charliermarsh]

Thanks!