Fix renderer typing, preserve message text, and harden crypto key handling

Fix abstract renderer signatures and add small stubs so type checkers can
see expected attributes (e.g. username, _decrypt). This removes several
mypy false-positives that were caused by mixin/ABC mismatches.
Preserve message text containing ':' by using split(':', 1) in both
DefaultClientRenderer and RichClientRenderer.
Normalize renderer APIs: print_chat(...) now takes the response mapping
and returns None (matches runtime behavior).
Make RSA symmetric-key request more robust: read r.content instead of a
fixed-size r.raw.read(999), avoiding truncated key material.
Improve _connect_ws exception handling in client to ensure a valid
Exception is re-raised if connection attempts fail.
Correct server/service typing: memory_msgs is now typed as
list[Message] and we null-check incoming payload text before creating a
new Message.
Replace manual package list in setup.py with setuptools.find_packages()
so packaging uses valid Python package names.
Installed types-requests in the project venv so mypy no longer flags the
requests import.
Verification: ran python -m compileall and mypy cmd_chat — no issues
remain.
Notes:

Wire format still uses Python literal evaluation in some places (existing
behavior); switching to JSON for client/server payloads is recommended as a
follow-up for robustness and security.

cmd_chat/server/server.py

@@ -40,7 +40,10 @@ def attach_endpoints(app: Sanic):
         while True:
             serialized_message: dict = await _get_bytes_and_serialize(ws)
             await _check_ws_for_close_status(serialized_message, ws)
-            new_message = await _generate_new_message(serialized_message.get("text"))
+            text = serialized_message.get("text")
+            if text is None:
+                continue
+            new_message = await _generate_new_message(text)
             MESSAGES_MEMORY_DB.append(new_message)
             await ws.send(str({"status": "ok"}))
             await asyncio.sleep(0.2)