benchmarker: Add result history and run metadata to stats panel

[Colton127]

Summary

This change adds persistent result history and detailed run metadata to the benchmarker's statistics panel, allowing users to view and compare past benchmark runs without re-running them.

Key Changes

• New BenchmarkResult class: Encapsulates a complete benchmark run including stats, configuration, timing information, and build mode. Replaces the previous pattern of passing individual parameters.

• Result history tracking: The BenchmarkController now maintains a list of completed runs (_results) with unique IDs, allowing users to select and compare past results from a dropdown menu.

• Enhanced StatsPanel UI:

  • Added a Result dropdown showing all completed runs in the session (newest first), with the run in flight listed above recorded ones
  • Added run metadata display showing start/end times, wall-clock duration, and build mode
  • Added a delete button to remove individual results or clear all history
  • Added "Export all results as JSON" option to copy multiple runs at once
  • Improved copy menu with per-option enable/disable states

• Build mode tracking: Introduced BuildMode enum (debug/profile/release) to track and display the compilation mode, since results are only comparable within the same mode.

• Report generation updates: Refactored buildJsonReport() and buildTextReport() to accept BenchmarkResult objects instead of individual parameters. Added buildJsonReportList() for exporting multiple results.

• Controller enhancements:

  • Added selectResult(), deleteResult(), and clearResults() methods for history management
  • Added liveResult property for the run in flight and selectedResult for the UI's displayed result
  • Added statusLabel property that includes worker count for running phases
  • Results are automatically recorded when a run reaches a terminal phase (finished/cancelled/failed)

• Improved logging: Run numbers and timestamps are now logged, with wall-clock duration reported at completion.

Notable Implementation Details

• The stats panel follows the live run by default but can be pinned to a historical result via the dropdown
• A run in flight is not yet recorded, so it cannot be deleted until it completes
• History is session-only (in-memory); it clears when the app closes
• Wall-clock duration includes cache preparation time, making it longer than the measured request time
• The UI gracefully handles empty history and disabled states for buttons when no results exist