simplex-chat-python: split Client from Bot, add request/response API (#6976)

* simplex-chat-python: split Client from Bot, add request/response API

Client is now the base class for SimpleX participants that talk TO
services (monitors, probes, automated participants). Bot extends Client
with server features (address, auto-accept, welcome, commands).

New methods on Client (inherited by Bot):
  connect_to(link)           idempotent contact handshake
  send_and_wait(id, text)    send a message and await the reply
  events()                   async iterator over chat events
  @on_message(contact_id=N)  filter by sender in decorators

BotProfile renamed to Profile (alias kept). New ContactAlreadyExistsError
subclass for cleaner error handling.

* simplex-chat-python: narrow event payload type per @on_event tag

@client.on_event("contactConnected") now types the handler's event
parameter as CEvt.ContactConnected instead of the unnarrowed
CEvt.ChatEvent union — mirroring how @on_message narrows by
content_type.

The 50 overloads are generated by the Haskell codegen into _events.py
(as a Protocol class), so new events stay in sync automatically.
Client.on_event is exposed as a property typed as that Protocol; the
runtime implementation is unchanged.

packages/simplex-chat-python/src/simplex_chat/__init__.py

@@ -1,12 +1,21 @@
 """SimpleX Chat — Python client library for chat bots."""
 
 from ._version import __version__
-from .api import ChatApi, ChatCommandError, ConnReqType, Db, PostgresDb, SqliteDb
+from .api import (
+    ChatApi,
+    ChatCommandError,
+    ConnReqType,
+    ContactAlreadyExistsError,
+    Db,
+    PostgresDb,
+    SqliteDb,
+)
 from .bot import (
     Bot,
     BotCommand,
     BotProfile,
     ChatMessage,
+    Client,
     CommandHandler,
     EventHandler,
     FileMessage,
@@ -16,6 +25,7 @@ from .bot import (
     MessageHandler,
     Middleware,
     ParsedCommand,
+    Profile,
     ReportMessage,
     TextMessage,
     UnknownMessage,
@@ -35,8 +45,10 @@ __all__ = [
     "ChatCommandError",
     "ChatInitError",
     "ChatMessage",
+    "Client",
     "CommandHandler",
     "ConnReqType",
+    "ContactAlreadyExistsError",
     "CryptoArgs",
     "Db",
     "EventHandler",
@@ -49,6 +61,7 @@ __all__ = [
     "MigrationConfirmation",
     "ParsedCommand",
     "PostgresDb",
+    "Profile",
     "ReportMessage",
     "SqliteDb",
     "TextMessage",