new gcs evaluator - attempt at fixing performance issue introduced via gcsl rework

[srliao]

This PR rewrites the gcs evaluator to remove the use of channel for blocking purposes (not truly a concurrent workload) which adds a lot of overhead as a result of context switching

[srliao]

on hold for now because it looks like this might actually be a performance decrease for wasm. needs more testing

also need to fix env scoping which is causing issues with closures not behaving properly