Remove follow_wrapped=False when getting signatures

[JelleZijlstra]

In signature.py, we use follow_wrapped=False when getting the signature of a callable:

pyanalyze/pyanalyze/arg_spec.py

Line 449 in 2ae6915

return inspect.signature(obj, follow_wrapped=False)

It would be nice if we don't, because that will allow us to get accurate signatures for more decorated functions. When I tried this, it caused problems with some decorators that modify the function's signature but use @functools.wrap, notably @mock.patch (which passes additional arguments to the decorated function). I've also run into issues with @contextlib.contextmanager, which changes the return type of the decorated function.

Possible solutions:

• Modify these decorators to set an accurate .__signature__ attribute on the decorated function (but that's not an option for third-party decorators)
• Add special casing for some of these. For example, patched functions have a .patchings attribute; we could internally ignore the parameter corresponding to any entries in .patchings that have their .new attribute set to mock.DEFAULT. But there doesn't seem to be a similar way to identify a function that was decorated with @contextmanager.

[JelleZijlstra]

#471 found a concrete place where this costs us type checking capabilities in pyanalyze's self check: methods annotated with qcore.caching.cached_per_instance().