fix: add type hints to ClientOptions (#735)

* Update

* Update client_options.py

* Update

* fix build

---------

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

Author: rinarakaki

Diff for: google/api_core/client_options.py

@@ -48,18 +48,20 @@ def get_client_cert():
 
 """
 
+from typing import Callable, Mapping, Optional, Sequence, Tuple
+
 
 class ClientOptions(object):
     """Client Options used to set options on clients.
 
     Args:
         api_endpoint (Optional[str]): The desired API endpoint, e.g.,
             compute.googleapis.com
-        client_cert_source (Optional[Callable[[], (bytes, bytes)]]): A callback
+        client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]): A callback
             which returns client certificate bytes and private key bytes both in
             PEM format. ``client_cert_source`` and ``client_encrypted_cert_source``
             are mutually exclusive.
-        client_encrypted_cert_source (Optional[Callable[[], (str, str, bytes)]]):
+        client_encrypted_cert_source (Optional[Callable[[], Tuple[str, str, bytes]]]):
             A callback which returns client certificate file path, encrypted
             private key file path, and the passphrase bytes.``client_cert_source``
             and ``client_encrypted_cert_source`` are mutually exclusive.
@@ -88,15 +90,17 @@ class ClientOptions(object):
 
     def __init__(
         self,
-        api_endpoint=None,
-        client_cert_source=None,
-        client_encrypted_cert_source=None,
-        quota_project_id=None,
-        credentials_file=None,
-        scopes=None,
-        api_key=None,
-        api_audience=None,
-        universe_domain=None,
+        api_endpoint: Optional[str] = None,
+        client_cert_source: Optional[Callable[[], Tuple[bytes, bytes]]] = None,
+        client_encrypted_cert_source: Optional[
+            Callable[[], Tuple[str, str, bytes]]
+        ] = None,
+        quota_project_id: Optional[str] = None,
+        credentials_file: Optional[str] = None,
+        scopes: Optional[Sequence[str]] = None,
+        api_key: Optional[str] = None,
+        api_audience: Optional[str] = None,
+        universe_domain: Optional[str] = None,
     ):
         if client_cert_source and client_encrypted_cert_source:
             raise ValueError(
@@ -114,11 +118,11 @@ def __init__(
         self.api_audience = api_audience
         self.universe_domain = universe_domain
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return "ClientOptions: " + repr(self.__dict__)
 
 
-def from_dict(options):
+def from_dict(options: Mapping[str, object]) -> ClientOptions:
     """Construct a client options object from a mapping object.
 
     Args: