chore: make env mode strict by default (#8182)
### Description
Commandeered from #8151
Changes default env mode to strict and remove the "infer" option
### Testing Instructions
Existing test suite
(Currently some Windows integration tests are failing due to a missing
env var, opening for review while I work on this)
---------
Co-authored-by: nicholaslyang <nicholas.yang@vercel.com>
