Support signatures with PEP 649 deferred annotations

[Otto-AA]

Draft for fixing #463

Python 3.14 supports deferred annotation loading. However, the inspect.signature raises an Error when trying to compute non-existing lazy-loaded annotations (which happens with if TYPE_CHECKING imports)

def foo(x: HelloWorld): pass
def bar(x: dict[str, int]): pass

# that's what we currently do
mutated_foo.__signature__ = signature(foo) # NameError: name 'HelloWorld' is not defined

# we can work around this by loading the annotation as a string, instead of evaluating it
from inspect import signature, Format

# using Format.STRING successfuly get's the format even if HelloWorld does not exist
print(signature(foo, annotation_format=Format.STRING)) # (x: 'HelloWorld')
# but it also stringifies the annotation, which we previously did not do
print(signature(bar, annotation_format=Format.STRING)) # (x: 'dict[str, int]')
print(signature(bar)) # (x: dict[str, int])

I guess changing from dict[str, int] to 'dict[str, int]' is no problem.

But we likely also want to set the mutated_foo.__annotations__ attribute?