perf: Reduce JSON validation during state updates

[FrederikBolding]

This PR makes two changes to improve performance in snap_setState and snap_manageState:

• Stop enforcing JSON sizing limits for preinstalled Snaps
• Stop double checking JSON validity in snap_setState

---

Note

Optimizes snap_setState/snap_manageState by using getSnap and getJsonSizeUnsafe to enforce size limits only for non-preinstalled Snaps, removes redundant JSON validation, updates hooks/simulation, adds TextEncoder allowances, and adjusts tests and coverage.

• RPC methods:
  • snap_setState (packages/snaps-rpc-methods/src/permitted/setState.ts): Add getSnap hook; replace getJsonSize with getJsonSizeUnsafe(..., true); enforce storage size only for non-preinstalled Snaps.
  • snap_manageState (packages/snaps-rpc-methods/src/restricted/manageState.ts): Add getSnap hook; move size check to method implementation using getJsonSizeUnsafe(..., true) (skip for preinstalled); validation now uses isValidJson and no longer checks size.
• Simulation:
  • Extend restricted hooks with getSnap and wire implementation (packages/snaps-simulation/src/simulation.ts).
• Utils:
  • Enhance getJsonSizeUnsafe to optionally measure byte length via TextEncoder and add tests (packages/snaps-utils/src/json.ts, json.test.ts).
• Security/Policies:
  • Allow TextEncoder in LavaMoat policies for @metamask/snaps-utils (iframe/node-process/node-thread/webview policies).
• Tests:
  • Update tests to use getSnap and cover large state error paths; remove size check from param validation (manageState.test.ts, setState.test.ts).
• Config:
  • Slightly raise Jest coverage thresholds (packages/snaps-rpc-methods/jest.config.js).

^{Written by Cursor Bugbot for commit 168610a. This will update automatically on new commits. Configure here.}

[FrederikBolding]

@metamaskbot update-pr

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.29%. Comparing base (0c693f0) to head (168610a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3660      +/-   ##
==========================================
+ Coverage   98.27%   98.29%   +0.01%     
==========================================
  Files         417      417              
  Lines       11902    11907       +5     
  Branches     1843     1848       +5     
==========================================
+ Hits        11697    11704       +7     
+ Misses        205      203       -2     

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