feat: improve `@llamaindex/env` #4211

Job	Run time
typecheck	53s
Build Core Example (cloudflare-worker-agent)	1m 30s
Test on Node.js 18.x	1m 45s
Build Core Example (nextjs-agent)	1m 44s
E2E on Node.js 18.x	1m 5s
Test on Node.js 20.x	1m 17s
typecheck-examples	1m 27s
Build Core Example (nextjs-edge-runtime)	1m 11s
E2E on Node.js 20.x	1m 0s
Test on Node.js 22.x	1m 38s
Build Core Example (waku-query-engine)	56s
E2E on Node.js 22.x	59s
	15m 25s

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