fix: cap uv concurrency to prevent ENFILE errors during bundling (#14)

When uv extracts many wheel files in parallel, the builder container can
exhaust the system-wide file descriptor limit (os error 23: Too many open
files), especially on Docker Desktop/macOS environments.

Add UV_CONCURRENT_DOWNLOADERS=4 and UV_CONCURRENT_BUILDS=2 to the builder
environment to limit uv's internal parallelism. This prevents the FD
exhaustion without meaningfully impacting performance, since most wheels
are served from cache on subsequent builds.

Fixes intermitent 'CommandExitedWithNonZeroStatus: docker exited with
status 1' errors caused by failed wheel extraction.

Co-authored-by: hermes-agent <hermes@hermes-agent.local>

Author: eoinsha-h

src/bundling.ts

@@ -365,6 +365,10 @@ function getBuilderEnvironment(
 ): Record<string, string> {
   return {
     UV_PYTHON_LAMBDA_NOFILE_LIMIT: BUILDER_NOFILE_LIMIT.split(':')[0],
+    // Cap uv concurrency to avoid system-wide file descriptor exhaustion
+    // during parallel extraction (os error 23: ENFILE).
+    UV_CONCURRENT_DOWNLOADERS: '4',
+    UV_CONCURRENT_BUILDS: '2',
     ...environment,
   };
 }