fix: Add top-level py.typed marker to resolve IDE import errors (#829)

## Changes

- Adds a `py.typed` marker at the root package level
(`src/auth0/py.typed`).

The marker previously only existed under `src/auth0/management/`,
causing IDEs like PyCharm to fall back to outdated [typeshed
stubs](python/typeshed#14697) and report
unresolved imports for `ManagementClient`, `ApiError`, and other
classes. A root-level marker signals IDEs to use the package's own
inline types instead.

Closes #824
Related: #804, #793

Author: kishore7snehil

.fernignore

@@ -16,8 +16,9 @@ CHANGELOG.md
 src/auth0/authentication/
 tests/authentication/
 
-# Root auth0 __init__.py
+# Root auth0 __init__.py and py.typed marker
 src/auth0/__init__.py
+src/auth0/py.typed
 
 # Telemetry customization (Auth0 format with dynamic versioning)
 src/auth0/management/core/client_wrapper.py