perf: optimize version checks and fix offline hang

[luigimasdea]

I was looking into the offline hang issue reported in #319. I saw that #320 attempts to fix it by adding a timeout, but it still relies on spawning a child_process.exec('npm view ...').

While a timeout fixes the infinite freeze, spawning a full npm child process is still very heavy and blocks the neu version command execution for a significant amount of time, even when the user is completely online.

Key Changes:

1. Removed child_process overhead: Replaced the npm view execution in src/utils.js with a lightweight https.get request directly to the npm registry API.
2. Concurrent network requests: Refactored src/commands/version.js to fetch the global, binary, and client library versions concurrently using Promise.all().
3. Offline handling: Added a 2-second timeout and proper .catch()/error handling to both checkLatestVersion (src/utils.js) and getRemoteLatestVersion (src/modules/downloader.js). If the network drops or is unreachable, the CLI instantly falls back to printing only the local versions without hanging.
4. Fixed false (latest) tags: Corrected the display logic. Previously, network failures defaulted to showing the (latest) tag. Now, offline states are handled as null and the CLI won't print false information.

Testing:

I ran the test suite locally, and all tests (including spec/misc.spec.js) pass successfully.

Closes #319