1/ Refactoring to prepare to support streamable transport

[jmorrell-cloudflare]

In preparation for supporting the streaming protocol, I've moved some things around to help the code "slot in" without disturbing the existing functionality.

• Rename McpAgent.mount to McpAgent.serveSSE with McpAgent.mount serving as an alias for backward compatibility.
• The DO will now store which protocol has been initiated. A session must always use the same protocol once it's been initialized. This is enforced by baking the protocol into the DO address: namespace.idFromName(`sse:${sessionId}`); however this is also enforced within the DO logic as well.
• When initializing the websocket connection between the worker and the DO, it used to pass the URL request through. Now we enforce that any request for an SSE transport has an /sse path. This will allow us to initialize the correct transport. This gives us space to accommodate an '/mcp' path for the streamable protocol. This change is entirely internal and not exposed to users.
• Better leverage the underlying Agent class to manage websocket connections. With the SSE transport, there is only one websocket connection, but this will become more important with the Streamable transport as there may be many more connections.

[changeset-bot]

🦋 Changeset detected

Latest commit: 82e3377

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
agents	Patch
hono-agents	Patch

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[threepointone]

closing this since it was landed in #186