perf: raise the worker young generation cap to 64MB

At 32MB, workers collected their young generation often enough to cost
6-8% at 4 threads. 64MB keeps most of the memory saved (26-34% at 4
threads) within 1-2.5% of `main`'s build time.

Assisted-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: ovflowd

.changeset/keep-memory-down.md

@@ -3,4 +3,4 @@
 '@doc-kit/generator-react': patch
 ---
 
-Builds use less memory, most of all with few threads: each worker's young generation is limited to 32MB, a single thread processes one chunk at a time and lets go of the pages' code before rendering them, and Vite's native bundler gets as many threads as doc-kit and returns the memory it frees. On the Node.js API docs, `--threads 1` now builds with Node.js's `--max-old-space-size=512`.
+Builds use less memory, most of all with few threads: each worker's young generation is limited to 64MB, a single thread processes one chunk at a time and lets go of the pages' code before rendering them, and Vite's native bundler gets as many threads as doc-kit and returns the memory it frees. On the Node.js API docs, `--threads 1` now builds with Node.js's `--max-old-space-size=512`.

packages/core/src/threading/constants.mjs

@@ -21,4 +21,4 @@ export const WORKER_HEAP_SIZE = 512;
  * from the machine's memory, as if each worker were the only one, so it made up
  * over half of a worker's heap. Node.js's `--max-semi-space-size` replaces it.
  */
-export const WORKER_YOUNG_GENERATION_SIZE = 32;
+export const WORKER_YOUNG_GENERATION_SIZE = 64;