Make random_search() return a CompilerEnv.

[ChrisCummins]

No description provided.

[codecov-commenter]

Codecov Report

Merging #387 (977485c) into development (a8408e8) will decrease coverage by 0.26%.
The diff coverage is 25.00%.

@@               Coverage Diff               @@
##           development     #387      +/-   ##
===============================================
- Coverage        85.91%   85.64%   -0.27%     
===============================================
  Files               87       87              
  Lines             4743     4745       +2     
===============================================
- Hits              4075     4064      -11     
- Misses             668      681      +13     

Impacted Files	Coverage Δ
compiler_gym/bin/random_search.py	0.00% <0.00%> (ø)
compiler_gym/random_search.py	88.02% <100.00%> (-2.12%)	⬇️
compiler_gym/random_replay.py	84.21% <0.00%> (-15.79%)	⬇️
compiler_gym/util/logs.py	59.37% <0.00%> (-3.13%)	⬇️
compiler_gym/datasets/tar_dataset.py	96.38% <0.00%> (-1.21%)	⬇️

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