Feature: Add Todo & FIXME Tracker Feature (TodoFeature)

### Description
This feature request proposes adding a lightweight, built-in feature called `TodoFeature` to help developers easily track technical debt, pending tasks, and inline comments directly within their workspace.

### Proposed Changes
* **`src/todoFeature.ts`:** Introduce a new `TodoFeature` class implementing `vscode.Disposable` to scan workspace files for `TODO` and `FIXME` comments.
* **Command Palette Integration:** Register a command (`vscode-extras.runTodoCheck`) allowing users to manually trigger a workspace scan.
* **Output Channel Logging:** Log discovered items with file paths, line numbers, and content into the log channel.
* **Configuration Toggle:** Add an enable/disable configuration setting (`vscode-extras.todoFeature.enabled`).

### Benefits
Provides a zero-dependency way to audit code comments and manage TODO items without needing external extensions.