perf: Add more tracing spans into startup path (#11965)
## Summary
- `--profile` previously had no visibility into pre-execution phases,
making it impossible to diagnose startup overhead
- Adds `info`-level tracing spans to every significant phase between
process start and task execution
- All spans appear in both the chrome trace JSON and the generated
markdown summary
## What this revealed
On this repo with `turbo run check-types --skip-infer --profile`:
| Phase | Time | % |
|---|---|---|
| `visit` (task execution) | 767.8ms | 79.5% |
| `build_http_client` (TLS init) | 96.5ms | 10.0% |
| `new_from_gix_index` (git index) | 48.5ms | 5.0% |
| `compile_globs` | 38.0ms | 3.9% |
| `find_untracked_files` | 30.9ms | 3.2% |
| `fetch` (cache I/O) | 28.0ms | 2.9% |
TLS initialization alone accounts for 10% of the non-execution overhead
— even when remote caching is disabled. This data wasn't visible before.
## Testing
Verified `--profile=profile.json` produces spans for all new
instrumentation points. The `.json.md` summary correctly reports
self-time and call trees for the new spans.
