fix!: require Node.js versions with ESM cluster support (#3348)

fix!: require Node.js versions with ESM cluster support (#3348)

* fix!: require Node.js versions with ESM cluster support

Migrate cluster fixtures and benchmarks to ESM, retain explicit CommonJS coverage, and test the exact minimum Node.js releases in CI.

BREAKING CHANGE: Node.js ^22.18.0 || >=24.3.0 is required. Upgrade older Node.js installations before updating Poolifier.

Fixes #782

* fix(examples): remove CommonJS cluster build workarounds

Build and start all six cluster and hybrid server examples as ESM. Remove redundant start:esm scripts and extension-dependent worker paths; retain public CommonJS library support.

* fix(examples): declare Node.js requirements for ESM cluster workers

Align the six standalone cluster and hybrid examples with the supported Node.js range. This declares compatibility and enables package-manager engine checks without adding a runtime guard or changing dependencies.

* docs: remove unnecessary ESM background from README

* docs: remove unnecessary cluster startup explanations