feat(relay-test-utils): add persistent resolvers support

[sjwilczynski]

Summary

Adds support for "persistent resolvers" in relay-test-utils - resolvers that are not removed from the queue after execution. This is useful for Storybook scenarios - where the same resolver needs to handle multiple interactions because user can interact with the component by clicking around the UI.

New Features

• Per-resolver persistence: Use {resolver, persistent: true} wrapper to keep a resolver in the queue
• Environment-level default: Configure mockConfig: {defaultPersistentResolvers: true} to make all resolvers persistent by default
• Clear resolvers: New clearOperationResolvers() method to explicitly clear the resolver queue
• mockClear integration: mockClear() now also clears the resolver queue

API

// Non-persistent (default, current behavior)
environment.mock.queueOperationResolver(operation =>
  MockPayloadGenerator.generate(operation)
);

// Persistent resolver (new)
environment.mock.queueOperationResolver({
  resolver: operation => MockPayloadGenerator.generate(operation),
  persistent: true,
});

// Environment-level default (new)
const environment = createMockEnvironment({
  mockConfig: {
    defaultPersistentResolvers: true,
  },
});

// Clear all resolvers (new)
environment.mock.clearOperationResolvers();

Verification

• Added unit tests for persistent resolver behavior
• Added tests for defaultPersistentResolvers config option
• Added tests for clearOperationResolvers() method
• Added tests for mockClear() clearing resolvers