fix(typing): Make sure mypy types ffi and lib as Any to avoid typing errors (#6239)

Author: klochek

py/.gitignore

@@ -1,5 +1,6 @@
 # FFI
 sentry_relay/_lowlevel*
+!sentry_relay/_lowlevel.pyi
 
 # Wheels
 dist

py/sentry_relay/ _lowlevel.pyi

@@ -0,0 +1,11 @@
+# Type stub for the cffi-generated native module `sentry_relay._lowlevel`.
+#
+# At runtime `_lowlevel.py` does `lib = ffi.dlopen(...)`, so `lib`/`ffi` are
+# populated dynamically from the Rust; their attributes cannot be known statically.
+# Without this stub, mypy types `lib` as cffi's generic `_cffi_backend.Lib`,
+# which declares none of the `relay_*` functions and so generates errors.
+# Here, we type them as Any to avoid these errors.
+from typing import Any
+
+ffi: Any
+lib: Any