feat: add model caching and benchmarking utilities (#671)

* feat: add model caching and benchmarking utilities

- Add modelCache.ts for disk caching of model lists
- Add benchmark.ts for testing model speed/quality

* fix: address review feedback - async fs, multi-provider support, error handling

* feat: add /benchmark slash command and unit tests

* feat: add /benchmark slash command and unit tests

src/utils/model/modelCache.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it, beforeEach, afterEach, vi } from 'bun:test'
+import { isModelCacheValid, getCachedModelsFromDisk, saveModelsToCache } from '../model/modelCache.js'
+
+vi.mock('../model/ollamaModels.js', () => ({
+  isOllamaProvider: vi.fn(() => true),
+}))
+
+describe('modelCache', () => {
+  const mockModel = { value: 'llama3', label: 'Llama 3', description: 'Test model' }
+
+  describe('isModelCacheValid', () => {
+    it('returns false for non-existent cache', async () => {
+      const result = await isModelCacheValid('ollama')
+      expect(result).toBe(false)
+    })
+  })
+
+  describe('getCachedModelsFromDisk', () => {
+    it('returns null when not cache available', async () => {
+      const result = await getCachedModelsFromDisk()
+      expect(result).toBeNull()
+    })
+  })
+
+  describe('saveModelsToCache', () => {
+    it('has saveModelsToCache function', () => {
+      expect(typeof saveModelsToCache).toBe('function')
+    })
+  })
+})