Before fetching package metadata from the registry, stat the local cache
file and send its mtime as an If-Modified-Since header. If the registry
returns 304 Not Modified, read the local cache instead of downloading
the full response body. This saves bandwidth and latency for packages
whose metadata hasn't changed since the last fetch.
Registries that don't support If-Modified-Since simply return 200 as
before, so there is no behavior change for unsupported registries.
Replace node-fetch with native undici for HTTP requests throughout pnpm.
Key changes:
- Replace node-fetch with undici's fetch() and dispatcher system
- Replace @pnpm/network.agent with a new dispatcher module in @pnpm/network.fetch
- Cache dispatchers via LRU cache keyed by connection parameters
- Handle proxies via undici ProxyAgent instead of http/https-proxy-agent
- Convert test mocking from nock to undici MockAgent where applicable
- Add minimatch@9 override to fix ESM incompatibility with brace-expansion
