Add debug logs when writing to persistent storage (#18288)

Adds traceVerbose logging calls at the two write paths in
persistentState.ts:
- PersistentState.updateValue() - the core write path used by
  both global and workspace persistent state
- updateWorkspaceStateValue() - a separate direct write path

This makes it easier to diagnose issues related to persistent
storage writes, as requested in the issue.

Verified: eslint and prettier pass cleanly on the changed file,
tsc compiles with no errors, and pre-existing test failures in
testing/utils.unit.test.js were confirmed unrelated (same
failures occur with this change stashed out).

Author: Shriraj1901

src/client/common/persistentState.ts

@@ -6,7 +6,7 @@
 import { inject, injectable, named, optional } from 'inversify';
 import { Memento } from 'vscode';
 import { IExtensionSingleActivationService } from '../activation/types';
-import { traceError } from '../logging';
+import { traceError, traceVerbose } from '../logging';
 import { ICommandManager } from './application/types';
 import { Commands } from './constants';
 import {
@@ -43,6 +43,7 @@ export async function updateWorkspaceStateValue<T>(key: string, value: T): Promi
         throw new Error('Workspace state not initialized');
     }
     try {
+        traceVerbose(`Updating workspace persistent state for key [${key}]`);
         _workspaceKeys.push(key);
         await _workspaceState.update(key, value);
         const after = getWorkspaceStateValue(key);
@@ -85,6 +86,7 @@ export class PersistentState<T> implements IPersistentState<T> {
 
     public async updateValue(newValue: T, retryOnce = true): Promise<void> {
         try {
+            traceVerbose(`Updating persistent state for key [${this.key}]`);
             if (this.expiryDurationMs) {
                 await this.storage.update(this.key, { data: newValue, expiry: Date.now() + this.expiryDurationMs });
             } else {