Add Intel PT AUX trace range support

[namtran1812]

Summary

Add record-time Intel PT range gating using perf AUX actions.

This introduces -aux-range "(START STOP)", which resolves the selected symbols to runtime addresses and configures perf so that:

• Intel PT starts paused
• hitting START resumes AUX tracing
• hitting STOP pauses AUX tracing

The control events are emitted in the same perf event group as the Intel PT source.

Motivation

magic-trace currently relies on userspace snapshot/control paths for trigger-based workflows. perf's AUX pause/resume support allows tracing to be gated directly by perf events, avoiding unnecessary trace collection outside the selected region.

Implementation

• add typed AUX actions (start-paused, resume, pause)
• add breakpoint-backed AUX control events
• resolve AUX range symbols using the existing ELF/runtime address path
• support both run and attach
• reject AUX ranges when stacktrace sampling is selected
• add serialization and generated-perf-argument expect tests

Validation

• dune build @fmt passes locally
• git diff --check passes locally
• full tests cannot run on macOS because the locked dependency graph includes Linux-only Jane Street dependencies

Opening as draft to validate the full Linux build/test suite before marking ready.

[namtran1812]

Draft for validation: DCO is passing, but the Linux build workflow is currently blocked before any jobs are created, so I haven't received a compile/test result yet. I'll keep this in draft until CI and Intel PT validation are complete.