[ty] Improve diagnostics when NotImplemented is called

[AlexWaygood]

Summary

Fixes astral-sh/ty#1571.

I realised I was overcomplicating things when I described what we should do in that issue description. The simplest thing to do here is just to special-case call expressions and short-circuit the call-binding machinery entirely if we see it's NotImplemented being called. It doesn't really matter if the subdiagnostic doesn't fire when a union is called and one element of the union is NotImplemented -- the subdiagnostic doesn't need to be exhaustive; it's just to help people in some common cases.

Test Plan

Added snapshots

[astral-sh-bot]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[astral-sh-bot]

mypy_primer results

Changes were detected when running on open source projects

pywin32 (https://github.com/mhammond/pywin32)
- com/win32com/demos/excelRTDServer.py:239:15: error[call-non-callable] Object of type `NotImplementedType` is not callable
+ com/win32com/demos/excelRTDServer.py:239:15: error[call-non-callable] `NotImplemented` is not callable - did you mean `NotImplementedError`?
- com/win32com/demos/excelRTDServer.py:278:15: error[call-non-callable] Object of type `NotImplementedType` is not callable
+ com/win32com/demos/excelRTDServer.py:278:15: error[call-non-callable] `NotImplemented` is not callable - did you mean `NotImplementedError`?

No memory usage changes detected ✅