Refactor - Moves runtime_environment_key out of Config into a static variable

[Lichtso]

Having runtime_environment_key inside Config is a bit of leaky abstraction as it requires the outside user to choose a key randomly and according to PROGRAM_ENVIRONMENT_KEY_SHIFT. It also prevents Config::eq from working properly as two identical configs but with different random keys would be considered different.

[codecov-commenter]

Codecov Report

Merging #492 (161e5c9) into main (2fe4357) will decrease coverage by 0.01%.
The diff coverage is 92.30%.

@@            Coverage Diff             @@
##             main     #492      +/-   ##
==========================================
- Coverage   89.65%   89.64%   -0.01%     
==========================================
  Files          23       23              
  Lines       10145    10150       +5     
==========================================
+ Hits         9095     9099       +4     
- Misses       1050     1051       +1     

Files Changed	Coverage Δ
src/jit.rs	92.45% <91.66%> (-0.05%)	⬇️
src/vm.rs	73.36% <100.00%> (-0.12%)	⬇️