feat(Handler/Documents): Add document RPC handlers and Cocoon notification helpers

- Implement RPC handlers for `$tryOpenDocument`, `$tryCreateDocument`, `$trySaveDocument`, `$trySaveDocumentAs`, and `$saveAll` operations by dispatching corresponding effects through `AppRuntime`
- Add notification helpers (`notify_model_*`) that serialize document states and send `$accept...` messages via `vine::send_notification_to_sidecar` to keep Cocoon's extension host synchronized
- Introduce URI parsing utilities and text line/EOL detection to handle VS Code-compatible document identifiers
- Ensure proper DTO formatting using `$mid` markers and scheme/path/external URI components as defined in `extHost.protocol.ts`

This enables bidirectional document management between Mountain's core and Cocoon's extension host, critical for maintaining VS Code extension compatibility through the shim layer. The implementation leverages Land's effect system for state management while using Vine IPC for real-time synchronization of document changes, dirty states, and metadata updates.

Author: NikolaRHristov