gh-140677 Add heatmap visualization to Tachyon sampling profiler by pablogsal · Pull Request #140680 · python/cpython

Introduce a new --heatmap output format that provides line-by-line
execution visualization. The heatmap shows:

- Color-coded execution intensity for each line (cold → warm → hot → very hot)
- Inline sample counts and percentages per line
- Per-file statistics (total samples, hottest line)
- Interactive call graph navigation with caller/callee buttons
- Module type badges (stdlib, site-packages, project code)

Unlike flamegraphs which show call stacks and time distribution, heatmaps
excel at identifying hot code paths within files, understanding line-level
execution patterns, and navigating through call relationships.

Small changes:
- Change navigation button colors for dark theme
- Update toggle button colors and active-state text
- Add missing "→" in the Intensity legend

python#140680)

Co-authored-by: Ivona Stojanovic <stojanovic.i@hotmail.com>