[javascript] Optimize DataModel Notification Strategy

# Proposal: Optimize DataModel Notification Strategy

## Reason
The current `DataModel.notifySignals` implementation performs a linear scan of all registered signals to find descendants whenever a value is updated. This becomes a performance bottleneck as the number of reactive bindings grows.

## Design
1. **Trie Structure**: Replace the flat `Map` for signals with a Trie (Prefix Tree).
2. **Efficient Lookup**: When a path like `/user` is updated:
- **Bubble**: Traverse up the tree to notify ancestors.
- **Cascade**: Visit the subtree at `user` to notify all descendants.
3. **Complexity**: This reduces notification overhead from $O(N)$ (where $N$ is total signals) to $O(P + D)$ (where $P$ is path depth and $D$ is the number of actual descendants).

## Key Files
- `renderers/web_core/src/v0_9/state/data-model.ts`