Fix metamask extension detection

[chakra-guy]

Explanation

This PR refactor the extension detection code to use EIP-6963

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate

---

Note

Switches MetaMask extension detection to async EIP-6963 flow and updates SDK logic to await it; also improves MWP transport focus listener handling and adds a test platform mock.

• Platform (src/domain/platform):
  • Implement EIP-6963-based detection started at module load; expose hasExtension(): Promise<boolean> backed by a shared detectionPromise.
• SDK (src/multichain):
  • Await hasExtension() in transport selection (getStoredTransport) and connection flow (connect), including isDesktopPreferred logic.
• Transport (src/multichain/transports/mwp):
  • Track window focus listener with a saved handler and remove it on disconnect; minor cleanup.
• Tests:
  • Add tests/mocks/platform.ts to mock async hasExtension; include in tests/mocks/index.ts.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.99%. Comparing base (74f90c1) to head (4845d17).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1371   +/-   ##
=======================================
  Coverage   74.99%   74.99%           
=======================================
  Files         184      184           
  Lines        4519     4519           
  Branches     1108     1108           
=======================================
  Hits         3389     3389           
  Misses       1130     1130           

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[sonarqubecloud]

Quality Gate passed

Issues
6 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud