Bump version to 0.4.9.post1

Post-release carrying the MPL-2.0 relicence (and vendored-protos
Apache-2.0 boundary) into a published version. Chatto server is still
at 0.4.9, so per the version-tracks-Chatto policy this is a
chattolib-only .postN ship.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "chattolib"
-version = "0.4.9"
+version = "0.4.9.post1"
 description = "Async Python client library for the Chatto webchat Connect API"
 requires-python = ">=3.11"
 license = "MPL-2.0 AND Apache-2.0"