JSON statistics panel (advanced insights)

[parsapanahpoor]

• Issue Title: Add advanced JSON statistics and insights panel
• Description:
  Provide an optional statistics panel that gives insights into the JSON structure (counts, depth, type distribution, approximate size, etc.). This can build upon or extend any existing statistics feature.
• Tasks:
  • Compute basic metrics: total nodes, objects, arrays, max depth.
  • Compute per-type counts (string, number, bool, null, etc.).
  • Estimate JSON size in bytes/KB.
  • Display metrics in a compact panel next to or above the viewer.
  • Allow enabling/disabling the stats panel via a parameter.
  • Document the statistics feature and configuration.