fix: Add missing WS types and allow local URLs

[FrederikBolding]

Fixes a couple of issues after the merge of the WebSockets PR. Adds the proper types for the RPC methods and allows local WebSocket URLs in snap_openWebSocket.

Also fixes the formatting for Uri validation errors.

Closes #3457

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.21%. Comparing base (1f4fc7a) to head (149524a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3459   +/-   ##
=======================================
  Coverage   98.21%   98.21%           
=======================================
  Files         404      404           
  Lines       11314    11317    +3     
  Branches     1763     1764    +1     
=======================================
+ Hits        11112    11115    +3     
  Misses        202      202           

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