fix: Stop relying on account metadata for MultichainRoutingService

[FrederikBolding]

Stop relying on account.metadata.snap.enabled for MultichainRoutingService as it is going away. Instead we can cross-check getRunnableSnaps.

While doing this fix I also managed to re-use getSupportedAccountsMetadata in more cases.

https://consensyssoftware.atlassian.net/browse/WPC-988

---

Note

Medium Risk
Changes routing eligibility checks for account Snaps by cross-referencing SnapController:getRunnableSnaps, which could impact which accounts/methods are considered routable if Snap/account metadata is inconsistent. Touches request routing and scope support detection, so regressions would affect multichain RPC handling.

Overview
Stops relying on account.metadata.snap.enabled (and other snap metadata fields) to decide whether an account Snap can service a request, and instead gates supported accounts by whether their metadata.snap.id appears in SnapController:getRunnableSnaps.

Refactors MultichainRoutingService to reuse #getSupportedAccountsMetadata for both request routing (#getSnapAccountId) and isSupportedScope, and extends it with an optional method filter.

Updates multichain test fixtures and InternalAccount typing to remove the deprecated metadata.snap.enabled/name fields, and adjusts tests to mock SnapController:getRunnableSnaps (including updated call ordering expectations).

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[FrederikBolding]

This is quite a bit more complicated to read now, but potentially worth it for the re-use?

[ccharly]

I wonder if flipping the expression would make it slightly more readable? 🤔 like:

          account.metadata.snap?.id !== undefined &&
          runnableSnaps.includes(account.metadata.snap?.id) &&
          (method === undefined || account.methods.includes(method))

I assume the compiler will "infer" that method cannot be undefined after the ||?

[ccharly]

(but IMO that's worth for the re-use yep)

[FrederikBolding]

Good point!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.56%. Comparing base (581474c) to head (a5425d0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3974   +/-   ##
=======================================
  Coverage   98.56%   98.56%           
=======================================
  Files         429      429           
  Lines       12363    12365    +2     
  Branches     1942     1944    +2     
=======================================
+ Hits        12185    12187    +2     
  Misses        178      178           

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[FrederikBolding]

This is slightly slower now since we do not use .some. We could duplicate the code to make it faster