fix: Validate origin in handleRequest

[FrederikBolding]

We were using empty origins in a lot of places instead of specifying metamask for internal requests. This PR disallows doing that so we can be clear about where requests are coming from. origin must now be either a valid URL or metamask.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.87%. Comparing base (1760a18) to head (8c8c495).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3292   +/-   ##
=======================================
  Coverage   94.87%   94.87%           
=======================================
  Files         517      517           
  Lines       11333    11335    +2     
  Branches     1748     1749    +1     
=======================================
+ Hits        10752    10754    +2     
  Misses        581      581           

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