chore(lint): Fix suppressed ESLint errors in permission-controller package

[Mrtenz]

Explanation

This fixes all suppressed ESLint errors in the permission-controller package.

References

Closes #7380.

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
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Adds explicit return types and stricter TypeScript typings across permission-controller (core, middleware, errors, tests), refactoring internals to private class fields and tightening APIs with minor non-functional changes.

• Core (permission-controller):
  • Convert internals to private class fields (e.g., #caveatSpecifications, #permissionSpecifications, #unrestrictedMethods) and private helpers (e.g., #getPermissionSpecification, #validatePermission, #requestUserApproval).
  • Add explicit return types and generics throughout (controllers, caveat decorators, mergers, mutators, helpers).
  • Initialize CaveatMutatorOperation enum values and tighten types for caveat merging, construction, and validation.
  • Use nullish coalescing in SubjectMetadataController.addSubjectMetadata and refactor cache/trim logic with private fields and static #getTrimmedState.
  • Ensure decorateWithCaveats wrapper has explicit Promise<Json> return.
• Middleware:
  • Introduce ExecuteRestrictedMethod type; pass executeRestrictedMethod via factory; tighten middleware typings and undefined-result handling.
• Errors:
  • Type return values for unauthorized, methodNotFound, and invalidParams; import needed types from @metamask/rpc-errors.
• Tests:
  • Add explicit return types, stronger typings for mocks/utilities, optional chaining for side-effect handlers, and minor refactors in test helpers.
• Config:
  • Remove permission-controller entries from eslint-suppressions.json for resolved rules.

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