[SEM-5] Add Policy Enforcement to WDK Core

[nimdeveloper]

Add registerPolicies

Summary

This PR introduces a policy engine to WDK via registerPolicies, enabling runtime enforcement of constraints on mutating wallet operations. Policies can be scoped by blockchain and method, support async evaluation, and execute deterministically with short-circuit rejection.

Key Changes

• New API: registerPolicies(policies) (chainable)

• Policy shape:

  interface Policy {
    name: string;
    target?: {
      wallet?: string;
      protocol?: {
        blockchain?: string;
        label?: string;
      };
    };
    method?: string | string[];
    evaluate({
      method: string,
      params: any,
      target: {
        wallet?: string;
        protocol?: {
          blockchain?: string;
          label?: string;
        };
      },
    }): boolean | Promise<boolean>;
  }

• Method wrapping: Only mutating methods are wrapped; no double wrapping.

• Error handling: Introduced PolicyViolationError for explicit rejection signalling.

• Async support: Fully supported in evaluate.

Tests & Documentation

• Comprehensive Jest test suite covering validation, filtering (wallet/method), stacking, short-circuiting, async evaluation, and isolation.
• Coverage reporting integrated in CI.
• Documentation updated with usage patterns and examples.

Impact

No breaking changes. Existing behaviour remains unchanged unless policies are registered.

This lays the foundation for configurable wallet governance (e.g., limits, whitelists, compliance rules) without coupling policy logic to protocol implementations.