StoneCypher / jssm / 777fac9d92f43ae898394bfcaa637a0cc324ef17

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feat(perf): per-package size archaeology collector + nightly workflow (fsl#1965)

collect_package_sizes.cjs builds the raw data behind the stacked-area
package-size charts: for every published version of each tracked package
(the jssm family), the uncompressed byte size of every file that version
shipped. One version-keyed JSON per package, each version carrying its ISO
publish time (the charts stack on a time axis, since independently-versioned
packages share no version axis). Stores ground truth only — family, colour,
and install-policy are derived downstream, never baked in, because those
eras get reorganised repeatedly (jssm-viz standalone -> embedded -> split).

Dependency-free: registry packument, built-in gunzip, a small tar reader
(validated byte-exact against a real jssm tarball: 61/61 files, total ==
unpackedSize). Append-only and authoritative-once-written; a version already
recorded is never re-fetched. Tarball fetches fan out through a bounded
sliding-window pool (--concurrency, default 12) with per-item error
isolation and periodic checkpoint writes, so the ~515-version first backfill
runs in ~75s and resumes forward if interrupted. A package that 404s
(unpublished, e.g. jssm-fence pre-v6) is skipped cleanly.

package_sizes.yml keeps the archive current on the perf_results branch
(checked out into a subdir, mirroring the graviton flow): first run
backfills all history, nightly runs append only new versions. 12 unit tests
cover arg parsing, the octal/tar readers, and the pool's bound + error
isolation.

Note: this is the data layer; wiring it into make_perf_chart.cjs as the two
stacked-area charts (jssm proper + ecosystem) is the next piece.

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