fix(langgraph): silence no-empty-function on AgentRef test stubs

CI's Library job failed lint on these pre-existing stub methods. The
empty bodies are intentional — they implement the AgentRef surface
for the adapter under test. Scope the disable to the stub helpers.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: blove

libs/langgraph/src/lib/to-chat-agent.conformance.spec.ts

@@ -6,6 +6,7 @@ import { signal } from '@angular/core';
 import { ResourceStatus } from './agent.types';
 import type { AgentRef } from './agent.types';
 
+/* eslint-disable @typescript-eslint/no-empty-function */
 function minimalRef(): AgentRef<unknown, any> {
   return {
     value:           signal<unknown>({}),

libs/langgraph/src/lib/to-chat-agent.spec.ts

@@ -7,6 +7,7 @@ import type { AgentRef, CustomStreamEvent } from './agent.types';
 import { ResourceStatus } from './agent.types';
 import { toChatAgent } from './to-chat-agent';
 
+/* eslint-disable @typescript-eslint/no-empty-function */
 function stubAgentRef(overrides: Partial<AgentRef<unknown, any>> = {}): AgentRef<unknown, any> {
   return {
     value:           signal<unknown>(null),