fix(cli): restore cluster namespace import to fix startup regression

[fuleinist]

Problem

PR #2763 reports that Prism 5.15+ fails to start in any mode (mock, proxy, etc.):

TypeError: Cannot read properties of undefined (reading 'isPrimary')
    at createMultiProcessPrism (packages/cli/dist/util/createServer.js:29:32)

Root cause

PR #2752 (Node 18 → 24 bump) changed the cluster import style from
namespace to default:

-import * as cluster from 'cluster';
+import cluster from 'node:cluster';

Under module: commonjs + esModuleInterop: false, the default import
compiles to node_cluster_1.default.isPrimary, but node_cluster_1.default
is undefined at runtime because the cluster module has no default export.
The namespace import compiles to cluster.isPrimary, which works because
the module IS the singleton Cluster instance.

Fix

Restore the namespace import with a type cast to satisfy the Cluster type
from @types/node 24+ (which only exposes the Cluster interface via the
default export). The cast is erased at compile time; runtime behavior is
identical to a plain namespace import.

import * as clusterNS from 'node:cluster';
const cluster = clusterNS as unknown as typeof import('node:cluster').default;

Verification

cluster.isPrimary === true            // was undefined before fix
typeof cluster.setupPrimary === 'function'
typeof cluster.fork       === 'function'

Pre-existing TypeScript errors in paths.ts, forwarder/index.ts, and
validator/index.ts (unrelated to this fix) remain unchanged.

Fixes #2763

[fuleinist]

Hi maintainers — gentle ping on this PR. It fixes a startup regression (#2763) where Prism 5.15+ crashes with TypeError: Cannot read properties of undefined (reading 'isPrimary') due to the Node 18→24 cluster import change.

The fix is a 10-line change in a single file (packages/cli/src/util/createServer.ts): restores the namespace import with a type cast that's erased at compile time. All CI checks pass.

Would appreciate a review when you have a moment. Thanks!

[fuleinist]

Hi maintainers — gentle ping on this PR. It restores the cluster namespace import to fix a startup regression. CI checks pass and the PR is mergeable. Would appreciate a review when you have a moment. Thanks!

[fuleinist]

Ping: this is a 10-line regression fix for Prism 5.15+ startup failure (#2763). CI is green. Would appreciate a review when you have a moment — the fix restores the namespace import style that the Node 18→24 bump accidentally broke.