Add getReactionStats Method for Time-Based Analysis

[Silent-Watcher]

Feature: Add getReactionStats Method for Time Periods

Description:
Add a method getReactionStats(reactableId, startDate, endDate) that returns reaction counts broken down by time periods (e.g., daily or weekly) within a date range.

Acceptance Criteria:

• Method exists: Model.getReactionStats(reactableId, startDate, endDate, interval?).
• Returns an array of objects with date, reaction, and count properties.
• The interval parameter can be day, week, or month.
• Uses MongoDB's date aggregation operators.
• Tests are added for this method.
• Add usage examples in docs