perf(ts): denoise baseline mem usage

TS_NODE_TRANSPILE_ONLY=true
Use v8 heap stats instead of memory usage (isolate vs process heap)
Baseline before each bench iter and tracking delta

# Current main
McapStreamReader
        3.01±0.08 op/s  Heap Used: 268.92±3.81 MB/op    Heap Total: 297.93±4.13 MB/op   ArrayBuffers: 213.39±2.40 MB/op
McapIndexedReader
        2.13±0.01 op/s  Heap Used: 284.31±3.36 MB/op    Heap Total: 316.23±1.45 MB/op   ArrayBuffers: 107.06±0.00 MB/op
McapIndexedReader_reverse
        2.14±0.02 op/s  Heap Used: 280.16±3.09 MB/op    Heap Total: 315.45±0.79 MB/op   ArrayBuffers: 107.06±0.00 MB/op

# New heap baseline (ts-node transpile only + delta tracking)
McapStreamReader
        3.44±0.03 op/s  Heap Used: 51.80±12.44 MB/op    Heap Total: 42.89±11.53 MB/op   ArrayBuffers: 112.95±6.87 MB/op
McapIndexedReader
        2.16±0.01 op/s  Heap Used: 70.75±2.55 MB/op     Heap Total: 60.15±2.89 MB/op    ArrayBuffers: 17.86±0.76 MB/op
McapIndexedReader_reverse
        2.17±0.03 op/s  Heap Used: 59.98±2.50 MB/op     Heap Total: 40.93±1.26 MB/op    ArrayBuffers: 16.00±0.00 MB/op

# New baseline on first change (bigint pr)
McapStreamReader
        4.20±0.07 op/s  Heap Used: 35.31±2.60 MB/op     Heap Total: 28.69±2.44 MB/op    ArrayBuffers: 118.47±10.33 MB/op
McapIndexedReader
        2.58±0.01 op/s  Heap Used: 23.74±2.33 MB/op     Heap Total: 12.38±1.05 MB/op    ArrayBuffers: 1.42±3.41 MB/op
McapIndexedReader_reverse
        2.60±0.00 op/s  Heap Used: 24.55±0.72 MB/op     Heap Total: 14.05±0.32 MB/op    ArrayBuffers: 5.60±0.98 MB/op

foxglove / mcap

perf(ts): denoise baseline mem usage #1209