Fix FunctionMaker.create() with return type annotation (#138)

[apoorvdarshan]

Summary

FunctionMaker.create() raised a SyntaxError when the signature string contained a return annotation, e.g.:

FunctionMaker.create("add3(a: int, b: int) -> int", "return add(a, b)", evaldict={"add": add})

The parser assumed the signature always ended with ) and stripped the last character with rest[:-1], then unconditionally re-appended ) when emitting the def line. With a return annotation present, this produced invalid source such as:

def add3(a: int, b: int) -> in):
    return add(a, b)

which failed to compile. This matches the report in #138 (and the earlier acknowledgement in #114).

Fix

In FunctionMaker.create(), split the argument list from an optional -> ... return annotation using rest.rpartition(')'), and reattach the annotation after the closing paren when building the def line (via a %(return_annotation)s placeholder so it is substituted safely). Signatures without a return annotation are handled exactly as before (rpartition yields an empty tail), so behavior is unchanged for the existing case.

Tests / Verification

• Added ExtraTestCase.test_return_annotation covering both a signature without an annotation and one with a -> int return annotation. It fails on master with SyntaxError: unmatched ')' and passes with this change.
• Full suite green: python tests/test.py -v -> Ran 26 tests ... OK (including the doctest suite).
• Lint/type checks clean: flake8 (CI config), codespell (CI config), python -m mypy.stubtest decorator, and python -m mypy src/decorator/__init__.py all pass.
• Added a CHANGES.md entry under "Unreleased".

Disclosure: prepared with AI assistance; reviewed and verified locally.

[micheles]

Thanks for your contribution, you must understand that the decorator module is old and predates annotations