remove rlenv dep for tests

[HenriDeh]

This dependency was making the local testing of RLCore tedious due to compatibility problems. I copied the three environments used in the tests and removed the dependency.

[codecov]

Codecov Report

Merging #989 (698fd4b) into main (dd19ee0) will decrease coverage by 1.84%.
The diff coverage is 81.20%.

@@            Coverage Diff             @@
##             main     #989      +/-   ##
==========================================
- Coverage   13.58%   11.75%   -1.84%     
==========================================
  Files         222      219       -3     
  Lines        7609     7691      +82     
==========================================
- Hits         1034      904     -130     
- Misses       6575     6787     +212     

Files	Coverage Δ
...c/ReinforcementLearningCore/test/policies/agent.jl	94.73% <ø> (ø)
...forcementLearningCore/test/policies/multi_agent.jl	100.00% <ø> (ø)
...earningCore/test/environments/rockpaperscissors.jl	71.42% <71.42%> (ø)
...mentLearningCore/test/environments/randomwalk1D.jl	66.66% <66.66%> (ø)
...rcementLearningCore/test/environments/tictactoe.jl	89.01% <89.01%> (ø)

... and 62 files with indirect coverage changes