feat: Add middleware to validate wallet_snap permission request

[Mrtenz]

This adds middleware which validates wallet_snap permission requests. It ensures wallet_snap is not requested together with other permissions.

https://consensyssoftware.atlassian.net/browse/WPC-398

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Note

Medium Risk
Adds new request-validation middleware for wallet_requestPermissions, which can reject previously-accepted multi-permission requests that include wallet_snap and may impact dapp compatibility.

Overview
Adds a new JSON-RPC middleware (createWalletSnapPermissionMiddleware) that validates wallet_requestPermissions and throws invalidParams when wallet_snap is requested together with any other permission.

Exports the middleware via src/middleware/index.ts, adds unit tests covering rejection/allow cases, and nudges Jest coverage thresholds to account for the new test file.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.47%. Comparing base (ce80114) to head (8c88edc).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3838   +/-   ##
=======================================
  Coverage   98.47%   98.47%           
=======================================
  Files         429      430    +1     
  Lines       12421    12433   +12     
  Branches     1924     1929    +5     
=======================================
+ Hits        12231    12243   +12     
  Misses        190      190           

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[FrederikBolding]

Can v2 middlewares be dropped in where we need them in clients as-is?

[Mrtenz]

Yeah, there's a function to use it as legacy middleware.

[FrederikBolding]

We should probably make note to start converting our code to use v2