refactor: api_types/model: Move pre-ZFL53 lengths to api_types.

Comment adjusted; Final applied to new constants.

zulipterminal/api_types.py

@@ -6,7 +6,7 @@
 
 from typing import Any, Dict, List, Optional, Union
 
-from typing_extensions import Literal, NotRequired, TypedDict
+from typing_extensions import Final, Literal, NotRequired, TypedDict
 
 # These are documented in the zulip package (python-zulip-api repo)
 from zulip import EditPropagateMode  # one/all/later
@@ -22,6 +22,17 @@
 TYPING_STARTED_WAIT_PERIOD = 10
 TYPING_STOPPED_WAIT_PERIOD = 5
 
+
+###############################################################################
+# These values are in the register response from ZFL 53
+# Before this feature level, they had the listed default (fixed) values
+# (strictly, the stream value was available, under a different name)
+
+MAX_STREAM_NAME_LENGTH: Final = 60
+MAX_TOPIC_NAME_LENGTH: Final = 60
+MAX_MESSAGE_LENGTH: Final = 10000
+
+
 ###############################################################################
 # Core message types (used in Composition and Message below)
 

zulipterminal/model.py

@@ -31,6 +31,9 @@
 
 from zulipterminal import unicode_emojis
 from zulipterminal.api_types import (
+    MAX_MESSAGE_LENGTH,
+    MAX_STREAM_NAME_LENGTH,
+    MAX_TOPIC_NAME_LENGTH,
     Composition,
     EditPropagateMode,
     Event,
@@ -70,14 +73,6 @@
 
 OFFLINE_THRESHOLD_SECS = 140
 
-# Adapted from zerver/models.py
-# These fields have migrated to the API inside the Realm object
-# in ZFL 53. To allow backporting to earlier server versions, we
-# define these hard-coded parameters.
-MAX_STREAM_NAME_LENGTH = 60
-MAX_TOPIC_NAME_LENGTH = 60
-MAX_MESSAGE_LENGTH = 10000
-
 
 class ServerConnectionFailure(Exception):
     pass