Ensure edit correction isn't re-done after confirm.

- Edit corretion leans on LLM-isms to ensure we properly fix poorly escaped content. Beacues of this we need to ensure that we don't re-run edit correction in many cases.
  - To ensure this an `LruCache` has been added to capture intermediate steps of edit correction to avoid re-computations.
  - Max cache size is 50 currently. This means a user can have a muti-confirmation flow of 25 items without recomputing anything (assuming they all break edit correction).
- Laid some groundwork for future testing.

Part of https://github.com/google-gemini/gemini-cli/issues/484

packages/server/src/utils/LruCache.ts

@@ -0,0 +1,41 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+export class LruCache<K, V> {
+  private cache: Map<K, V>;
+  private maxSize: number;
+
+  constructor(maxSize: number) {
+    this.cache = new Map<K, V>();
+    this.maxSize = maxSize;
+  }
+
+  get(key: K): V | undefined {
+    const value = this.cache.get(key);
+    if (value) {
+      // Move to end to mark as recently used
+      this.cache.delete(key);
+      this.cache.set(key, value);
+    }
+    return value;
+  }
+
+  set(key: K, value: V): void {
+    if (this.cache.has(key)) {
+      this.cache.delete(key);
+    } else if (this.cache.size >= this.maxSize) {
+      const firstKey = this.cache.keys().next().value;
+      if (firstKey !== undefined) {
+        this.cache.delete(firstKey);
+      }
+    }
+    this.cache.set(key, value);
+  }
+
+  clear(): void {
+    this.cache.clear();
+  }
+}