fix: filter object env vars to prevent [object Object] in subprocess env

[aviu16]

Summary

• Fixes Bug: PM2 passes object properties as "[object Object]" environment variables to subprocesses #6073: PM2 passes object properties as [object Object] environment variables to subprocesses
• Adds Utility.sanitizeEnv() to filter pm2_env before passing to child_process.spawn() in ForkMode, keeping only primitive values (string, number, boolean)
• Adds Utility.isEnvSafeValue() helper to check if a value is safe for env var usage
• The 6 polluted env vars (env, axm_monitor, axm_options, axm_dynamic, axm_actions, node_args) are now properly excluded from the spawn environment

Root Cause

In lib/God/ForkMode.js, the entire pm2_env object (which contains nested objects) was passed directly as the env option to child_process.spawn(). Node.js spawn() calls .toString() on all env values, converting objects to the string "[object Object]".

Fix

Filter the environment object before passing it to spawn(), keeping only string, number, and boolean values. Numbers and booleans are explicitly converted to strings via String(). Objects, arrays, null, undefined, and functions are excluded.

Note: ClusterMode.js already handles this correctly by using JSON.stringify(env_copy) (line 48), so no changes were needed there.

Test plan

• Added 38 tests in test/programmatic/env_sanitization.mocha.js
  • Unit tests for Utility.sanitizeEnv() covering all value types
  • Unit tests for Utility.isEnvSafeValue() helper
  • PM2-specific scenario tests verifying the 6 known object keys are filtered
  • Edge case tests (null input, empty objects, NaN, Infinity, Date, RegExp)
  • Integration tests verifying forked processes start correctly with sanitized env
• All 38 tests passing
• Verified no [object Object] values appear in sanitized output

[CLAassistant]

All committers have signed the CLA.

[aviu16]

recheck

[aviu16]

quick ping here. if this needs adjustments, i can update fast.

[aviu16]

validated this branch with the dedicated sanitization suite:\n./node_modules/.bin/mocha test/programmatic/env_sanitization.mocha.js\n\nresult: 38 passing.\n\nthis includes integration assertions that forked processes start without [object Object] env pollution while preserving user-defined primitive env vars.

[aviu16]

Friendly bump on this PR. When maintainers have a moment, could someone please take a look? Happy to make any requested changes quickly. Thanks!