implement getenv and putenv in go (#1086)
* implement getenv and putenv in go
* fix typo
* apply formatting
* return a bool
* prevent ENV= from crashing
* optimization
* optimization
* split env workflows and use go_strings
* clean up unused code
* update tests
* remove useless sprintf
* see if this fixes the asan issues
* clean up comments
* check that VAR= works correctly and use actual php to validate the behavior
* move all unpinning to the end of the request
* handle the case where php is not installed
* fix copy-paste
* optimization
* use strings.cut
* fix lint
* override how env is filled
* reuse fullenv
* use corect function
