fix(handlers): sync MEDIA_BUY_STATE_MACHINE with spec v3 enum#289

bokelley merged 2 commits intomainadcontextprotocol/adcp-client-python:mainfrom

claude/issue-288-state-machine-pending-activationadcontextprotocol/adcp-client-python:claude/issue-288-state-machine-pending-activationCopy head branch name to clipboard