chore: revert version to 1.6.1 (release-please will manage version bumps)

Author: bokelley

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "adcp"
-version = "2.0.0"
+version = "1.6.1"
 description = "Official Python client for the Ad Context Protocol (AdCP)"
 authors = [
     {name = "AdCP Community", email = "maintainers@adcontextprotocol.org"}