Better tree hierarchy for trace view

[yurishkuro]

Which problem is this PR solving?

• Make tree hierarchy more useful and easier to navigate
• Resolves Trace - Indicate the number of descendants for a given row #176

Description of the changes

• uses boxes with direct children counts
• draws service-colored lines directly
• make inferred vs. own error icons display differently (hollow vs. solid exclamation icon)

How was this change tested?

[codecov]

Codecov Report

❌ Patch coverage is 97.67442% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 97.10%. Comparing base (1f98f5f) to head (6d3a15f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...nents/TracePage/TraceTimelineViewer/SpanBarRow.tsx	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3302      +/-   ##
==========================================
- Coverage   97.10%   97.10%   -0.01%     
==========================================
  Files         266      266              
  Lines        8359     8389      +30     
  Branches     2214     2231      +17     
==========================================
+ Hits         8117     8146      +29     
- Misses        239      240       +1     
  Partials        3        3              

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