Preserve function signature

[Otto-AA]

Closes #454 and #465 .

@boxed In case you want to review, this is a slightly bigger change of trampoline internals. This PR adds some complexity at the trampoline wrapper (handling various possible parameter formats, async declarations and async generators), but I think it's worth it so we can preserve the original function signature. Also, don't need to manually copy the signature with trampoline.__signature__ = inspect.signature(original_method) anymore.

With this change, asyncio.iscoroutinefunction(async_func) also returns true after we mutated the function. This is done by using the same signature as it was originally, and adding some logic to pass our arguments to the trampoline.

For instance:

async def foo(a: str, b, *args, **kwargs) -> dict[str, int]:
    # ...

Will be mutated to:

async def foo(a: str, b, *args, **kwargs) -> dict[str, int]:
    args = [a, b, *args]
    kwargs = {**kwargs}
    return await _mutmut_trampoline(x_foo__mutmut_orig, x_foo__mutmut_mutants, args, kwargs, None)

In the commit 944d43f, I've also added inline-snapshot (+ruff formatting for the snapshots) to make it easier to work with regression snapshots. e.g. the tests/test_mutation regression.py are useful to have and with inline-snapshot it's easier to update them whenever some implementation detail changes.

The e2e tests and a sample repository I tried were not affected by this change, so I don't think it breaks existing functionality.

[boxed]

Nice!