Resolve "Fix mypy errors in models.py and complete type hints"

Summary

This MR fixes many type errors in models.py reported by mypy (Related to #191 (closed))

Focus

• Potential Nones are now handled wherever mypy reported them
• Please check the correctness of IMPORTANCE vs INHERITANCE (see also server docs)
• New type hints for Query, QueryTemplate
• Two open issue remain (see below).

Test Environment

Regular

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• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
  • How do I develop or debug the software? Assume novice developers.
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
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For further good practices have a look at our review guidelines.

src/linkahead/common/models.py

@@ -1045,7 +1045,7 @@ out: List[Entity]
 
                     return p
         else:
-            raise ValueError("pattern argument should be Entity, int or str")
+            raise ValueError("`pattern` argument should be an Entity, int or str.")
 
         return None
 
@@ -3966,7 +3966,7 @@ class Container(list):
         else:
             entity._checksum = None
 
-    # FIXME: The signature of Conatiner.insert is completely different than the superclass'
+    # FIXME: The signature of Container.insert is completely different than the superclass'
     #        list.insert method. This may be a problem in the future, but is ignored for now.
     def insert(  # type: ignore
         self,
@@ -3981,20 +3981,23 @@ class Container(list):
         identified, retrieved, updated, and deleted via this ID until it has
         been deleted.
 
-        If the insertion fails, a LinkAheadException will be raised. The server will have returned at
-        least one error-message describing the reason why it failed in that case (call
+        If the insertion fails, a LinkAheadException will be raised. The server will have returned
+        at least one error-message describing the reason why it failed in that case (call
         <this_entity>.get_all_messages() in order to get these error-messages).
 
-        Some insertions might cause warning-messages on the server-side, but the entities are inserted
-        anyway. Set the flag 'strict' to True in order to force the server to take all warnings as errors.
-        This prevents the server from inserting this entity if any warning occurs.
+        Some insertions might cause warning-messages on the server-side, but the entities are
+        inserted anyway. Set the flag 'strict' to True in order to force the server to take all
+        warnings as errors.  This prevents the server from inserting this entity if any warning
+        occurs.
 
         @param strict=False: Flag for strict mode.
         @param sync=True: synchronize this container with the response from the server. Otherwise,
-                          this method returns a new container with the inserted entities and leaves this container untouched.
-        @param unique=True: Flag for unique mode. If set to True, the server will check if the name of the
-                            entity is unique. If not, the server will return an error.
+                          this method returns a new container with the inserted entities and leaves
+                          this container untouched.
+        @param unique=True: Flag for unique mode. If set to True, the server will check if the name
+                            of the entity is unique. If not, the server will return an error.
         @param flags=None: Additional flags for the server.
+
         """
 
         self.clear_server_messages()
@@ -4264,9 +4267,7 @@ class ACI():
             e.set("role", self.role)
         else:
             if self.username is None:
-                raise LinkAheadException(
-                    "An ACI must have either a role or a username."
-                )
+                raise LinkAheadException("An ACI must have either a role or a username.")
             e.set("username", self.username)
 
             if self.realm is not None: