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/client/client.py

@@ -40,7 +40,7 @@ class Client(RSAService, RichClientRenderer):
         return f"{self.ws_url}{path}"
 
     def _connect_ws(self, path: str, retries: int = 5, backoff: float = 0.5):
-        last_exc = None
+        last_exc: Exception = ConnectionError("Failed to connect")
         for attempt in range(retries):
             try:
                 return create_connection(self._ws_full(path))