[ty] Fix lookup of __new__ on instances

[AlexWaygood]

Summary

We weren't correctly modeling it as a staticmethod in all cases, leading us to incorrectly infer that the cls argument would be bound if it was accessed on an instance (rather than the class object).

Test Plan

Added mdtests that fail on main. The primer output also looks good!

[github-actions]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[github-actions]

mypy_primer results

Changes were detected when running on open source projects

pip (https://github.com/pypa/pip) - src/pip/_vendor/rich/style.py:478:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - src/pip/_vendor/rich/style.py:630:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - src/pip/_vendor/rich/style.py:653:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - src/pip/_vendor/rich/style.py:676:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - src/pip/_vendor/rich/style.py:734:41: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - Found 582 diagnostics + Found 577 diagnostics rich (https://github.com/Textualize/rich) - rich/style.py:478:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - rich/style.py:630:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - rich/style.py:653:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - rich/style.py:676:37: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - rich/style.py:734:41: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - Found 321 diagnostics + Found 316 diagnostics zope.interface (https://github.com/zopefoundation/zope.interface) - src/zope/interface/interface.py:739:16: error[missing-argument] No arguments provided for required parameters `bases`, `attrs` of bound method `__new__` + src/zope/interface/interface.py:739:16: error[missing-argument] No arguments provided for required parameters `name`, `bases`, `attrs` of function `__new__` pycryptodome (https://github.com/Legrandin/pycryptodome) - lib/Crypto/Hash/CMAC.py:173:28: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 1, got 2 - Found 1775 diagnostics + Found 1774 diagnostics sympy (https://github.com/sympy/sympy) - sympy/physics/secondquant.py:1983:45: error[too-many-positional-arguments] Too many positional arguments to bound method `__new__`: expected 2, got 3 - Found 14031 diagnostics + Found 14030 diagnostics 

No memory usage changes detected ✅