improve mwp connection management

[adonesky1]

Fix stuck CONNECTING state in MWPTransport

Problem

The MWPTransport.connect() method could leave the underlying DappClient stuck in a CONNECTING state, causing subsequent connection attempts to fail with "Cannot connect when state is CONNECTING".

Root Causes

1. No guard against concurrent connection calls – Multiple calls to connect() would attempt to call dappClient.connect() simultaneously
2. Message handler leak – The 'message' handler registered during connection was never removed, causing memory leaks and duplicate handlers on reconnection
3. Unhandled resume failures – If dappClient.resume() threw, the 'connected' event listener would hang indefinitely
4. Missing await on onResumeSuccess – Errors from this async function were not properly caught

Changes

• Add connectionPromise to track in-progress connections and return the existing promise on concurrent calls
• Track and clean up the connection message handler (connectionMessageHandler) on success, failure, timeout, and disconnect
• Handle resume() errors by removing the 'connected' listener and rejecting the promise
• Properly await onResumeSuccess() with .catch() to surface errors