fix: Fix broken wallet_sessionChanged listener when using underlying multichain-api-client's WindowPostMessageTransport

[jiexi]

Explanation

Fixes wallet_sessionChanged events not making it to the MultichainClient from the DefaultTransport because the underlying WindowPostMessageTransport has removed any event listeners when connect() is called on it and it is already connected. Should it be doing that, i'm not sure.

The workaround for now is to check if we are connected or not in the (multichain-api-client) transport used by the (our) DefaultTransport (not a good name...) before attempting to call connect() again.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes