Batch compatible statistics requests

[rosenrot00]

Summary

• Batch static statistics entities sharing the same period and time range into one recorder/statistics_during_period request.
• Keep dynamic or incompatible entities on the existing individual request path.
• Fall back to individual requests if batching fails.
• Add tests for batching, cache reuse, different periods, dynamic entities, and fallback behavior.

Motivation

Home Assistant supports multiple statistic_ids per request, but the card currently sends one request per trace. This reduces four compatible series from four requests to one without requiring configuration changes.

Testing

• npm run tsc
• 15 relevant Jest tests passed
• npm run build