Fix JMAP Fastmail client to properly connect to API
- Fix typo in URI from "sessio" to "session"
- Modify HTTP client to support both GET and POST methods as required by API
- Improve JSON parsing to handle null values in API responses
- Add detailed debug logging to help troubleshoot API interactions
- Update mailbox and email parsers to be more robust with server responses
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Co-Authored-By: Claude <noreply@anthropic.com>