fix: Add return type annotation to getCaip25PermissionFromLegacyPermissions

[MajorLift]

Explanation

This commit enables the return output of getCaip25PermissionFromLegacyPermissions to be assignable to RequestedPermissions.

Because RequestedPermissions is defined using NonEmptyArray, assigning ReturnType<typeof getCaip25PermissionFromLegacyPermissions> to RequestedPermissions currently results in the following error:

Type '{ "endowment:caip25": { caveats: { type: string; value: Caip25CaveatValue; }[]; }; }' is not assignable to type 'RequestedPermissions'.
  Property '"endowment:caip25"' is incompatible with index signature.
    Type '{ caveats: { type: string; value: Caip25CaveatValue; }[]; }' is not assignable to type 'Partial<PermissionConstraint>'.
      Types of property 'caveats' are incompatible.
        Type '{ type: string; value: Caip25CaveatValue; }[]' is not assignable to type '[CaveatConstraint, ...CaveatConstraint[]]'.
          Source provides no match for required element at position 0 in target.ts(2322)

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 communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes