refactor(log-viewer): drop the sprite timeline renderers

[lukecotter]

📝 PR Overview

Removes code the extension no longer runs. First of a planned series that reduces the
codebase: this PR is deletions and test-setup sharing only, so nothing a user can reach
changes.

The mesh renderers replaced the sprite ones some time ago — FlameChart uses
MeshRectangleRenderer, MeshMarkerRenderer and MeshAxisRenderer, and
SearchOrchestrator uses MeshSearchStyleRenderer. The sprite predecessors were never
deleted. They still compiled, still ran in CI, and no production file imported them.

🛠️ Changes made

• Delete the sprite render path: AxisRenderer (287), SearchStyleRenderer (209),
  TimelineMarkerRenderer (192), SpritePool (154), EventBatchRenderer (144).
  SpritePool's only importers were the other four.
• Delete markers.test.ts (699) and batching.test.ts (564), which constructed only
  those classes.
• Move the one behaviour that lost its only coverage — sortMarkersByTimeAndSeverity —
  into MarkerProcessor.test.ts, beside the other exports of that module.
• Repoint comments that named a deleted file. SearchHighlightRenderer's culling
  comments now name SelectionHighlightRenderer, which holds the identical
  implementation; MeshRectangleRenderer documents that it does not cull.

Net: −2,237 lines.

🧩 Type of change (check all applicable)

• 🐛 Bug fix - something not working as expected
• ✨ New feature – adds new functionality
• ♻️ Refactor - internal changes with no user impact
• ⚡ Performance Improvement
• 📝 Documentation - README or documentation site changes
• 🔧 Chore - dev tooling, CI, config
• 💥 Breaking change

📷 Screenshots / gifs / video [optional]

No UI change. The timeline renders through the mesh path before and after.

🔗 Related Issues

None.

✅ Tests added?

• 👍 yes

sortMarkersByTimeAndSeverity had no coverage outside the deleted markers.test.ts, so
it gains a case in MarkerProcessor.test.ts.

Coverage this PR gives up. markers.test.ts also covered marker viewport culling,
end-time resolution and per-type colour. Those cases asserted sprite tint, alpha, x
and width — internals of the deleted class — so they could not move across as written.
MeshMarkerRenderer keeps visibleIndicators private and had no suite of its own before
this PR either, so the gap is pre-existing rather than new, but it is not closed here.
The fix worth making is extracting MeshMarkerRenderer.render()'s pure per-marker block
into MarkerProcessor, where those three behaviours become directly testable. Filed as
follow-up, not done here.

batching.test.ts needs no replacement: TemporalSegmentTree.test.ts and
RectangleCache.bucket.test.ts already cover the culling, size classification and
bucketing it exercised, against the live path.

📚 Docs updated?

• 🙅 not needed

No user-visible change, so no CHANGELOG entry. README and help site untouched.

Anything else we need to know? [optional]

Verified with pnpm test (2,567 passing, 186 suites), pnpm lint (0 errors) and
pnpm build (all three bundles). The build is the load-bearing check here — rollup has
to resolve every import for the bundles to be produced.

Two pre-existing problems found while reviewing this change, both left alone:

• MetricStripRenderer.ts:471 re-sorts the marker array every frame ([...markers].sort)
  inside the 16.6ms budget, and exception markers are unbounded. Memoising on array
  identity is a three-line fix.
• SearchHighlightRenderer.ts:150 hardcodes const EVENT_HEIGHT = 15 where its twin
  uses TIMELINE_CONSTANTS.EVENT_HEIGHT, which that file already imports.

TimeGridCalculator.ts still carries four comments naming the deleted AxisRenderer.
The file has no importers at all and is deleted in the next commit on this branch, so the
comments go with it.

[lukecotter]

Refiling against certinia/debug-log-analyzer — that is where this should merge.