Add MemorySample to Turbopack trace infrastructure (#90597)
### What?
Adds periodic process memory sampling to the Turbopack trace system.
Two new capabilities:
1. **`TraceRow::MemorySample`** — A new trace row variant that captures
`TurboMalloc::memory_usage()` at ~10ms intervals
2. **`memory_samples`** **in** **`QueryResult`** — When querying a span,
returns up to 200 memory usage samples covering the span's time range
### Why?
To provide visibility into process memory usage over time in the
Turbopack trace viewer. Currently the trace system tracks per-span
allocations/deallocations but has no global memory usage timeline.
### How?
**Sampling (`turbopack-trace-utils`):**
- New `TraceRow::MemorySample { ts, memory }` variant
- Sampling triggered from `on_enter` using a three-tier dedup strategy
to minimize overhead:
1. Thread-local check (no synchronization)
2. Global atomic read (single load)
3. CAS to claim the sample (only one thread wins per interval)
- This ensures at most one sample per 10ms across all threads
**Storage (`turbopack-trace-server`):**
- Global sorted `Vec<(Timestamp, u64)>` in the `Store`
- Insertion-sort step on add (efficient since samples arrive nearly
sorted)
- Binary search for range queries
**Query (`turbopack-trace-server`):**
- `memory_samples_for_range(start, end)` returns up to 200 samples
- When more exist, merges groups of N by taking the max value per group
- Added `memory_samples: Vec<u64>` field to `QueryResult`
https://github.com/vercel/turbo-trace-viewer/pull/24
