#8883 Upgrade libuv to 1.53.0 via the rescript-lang/luv fork

The opam override for Luv now fetches commit 8c12b1a of rescript-lang/luv (PR rescript-lang/luv#2) instead of patching the upstream 0.5.14 tarball. The fork vendors libuv 1.53.0 instead of 1.48.0 and already carries the ARM64 musl -mno-outline-atomics fix, so the local patch is gone. The package is versioned 0.5.14+rescript.1 and dune-project/rescript.opam pin that version.

Review

• Why a git URL and not a release tarball? The fork keeps libuv as a git submodule; GitHub archives omit submodules, while opam's git fetch initializes them. The commit hash should move to the merge commit once rescript-lang/luv#2 lands.
• Does the OCaml rewatch use any changed Luv API? Only FS_event, Loop, Timer, Handle and Error (native_watcher.ml). The fork's API change (statfs reserved fields read as zero) does not reach it.

No effect

Output: unchanged

Tests

nonebecause no observable behavior changes; the shared rewatch suite (113 checks, incl. watch mode), the rewatch-ocaml focused suite and scripts/test.js -ounit -build -mocha -docstrings pass on the new libuv

Measured

• watch edit latency, median of 21 interleaved edits (basic fixture) 99 → 100 ms, A/A control 98 ms
• 400-directory fixture 98 → 102 ms, A/A control 100 ms
• watch cold start, median of 7 (400 dirs) 213 → 211 ms, A/A 212 ms
• idle watcher CPU over 20 s 70-90 ms for all
• clean build (400 modules), median of 9, 180 → 180 ms
• linux-arm64 devcontainer under load, job tmp watch_ab.py and clean_ab.py

• Changelog fragment changes/luv-libuv-1-53.internal.md
• No test changes, as recorded
• No committed generated JS changes

The Luv override now fetches 2094c025, the merge commit of rescript-lang/luv#2 and the fork's master tip, instead of the PR head 8c12b1a. Both commits have the same tree (7acc6c6d), so the built sources are identical.

No effect

Output: unchanged

Tests

nonebecause the fetched source tree is identical to the tested one

• No test changes, as recorded
• No committed generated JS changes