[ty] Diagnose invalid __getattr__ calls (#27502)
## Summary
Previously, an invalid `__getattr__` method caused us to report that the
requested attribute was missing, even though Python actually invokes the
method and raises `TypeError`:
```py
class Example:
def __getattr__(self) -> str:
return "fallback"
Example().missing # error: [invalid-attribute-access]
```
We now propagate failed implicit `__getattr__` calls through the
generalized member-lookup error introduced in #27400, so the diagnostic
identifies the invalid call and preserves the method's return type for
error recovery.
This applies to instance and metaclass attribute lookup, including
incompatible attribute-name parameters. Literal-restricted `__getattr__`
methods continue to treat unsupported names as missing attributes, and
already-defined attributes still bypass the fallback.
Closes https://github.com/astral-sh/ty/issues/135.
