fix(typing): Make sure mypy types ffi and lib as Any to avoid typing errors

[klochek]

I ran into bizarre typing errors while working on another PR, such as  py/sentry_relay/utils.py:13: error: "Lib" has no attribute "relay_init" [attr-defined]

I yolo'd Claude on this one, what it found seems plausible to me:

your pyproject.toml lists cffi_backend under ignore_missing_imports = true, so lib resolved to Any and every lib.relay* call was silently accepted. But a
_cffi_backend-stubs package is now installed in your venv (.venv/lib/python3.14/site-packages/_cffi_backend-stubs/, shipped by recent cffi). Once a stub is found, ignore_missing_imports
no longer applies — it only suppresses "module not found." That stub declares:

@Final
class Lib:
def dir(self): ...

So, looks like a recent devenv change surfaced this mypy issue. This PR appears to address it.