Limit the static paths worker number during development (#45344)

As per my testing, this saves about 150~210 MB memory for the dev server
as I have an 8-core CPU.

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ]
[e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs)
tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
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---------

Author: shuding

packages/next/src/server/dev/next-dev-server.ts

@@ -126,7 +126,9 @@ export default class DevServer extends Server {
       require.resolve('./static-paths-worker'),
       {
         maxRetries: 1,
-        numWorkers: this.nextConfig.experimental.cpus,
+        // For dev server, it's not necessary to spin up too many workers as long as you are not doing a load test.
+        // This helps reusing the memory a lot.
+        numWorkers: Math.min(this.nextConfig.experimental.cpus || 2, 2),
         enableWorkerThreads: this.nextConfig.experimental.workerThreads,
         forkOptions: {
           env: {