Test fixes and improvements

[ChrisCummins]

• Marks a couple of flaky tests (CI test failure: test_running_environment_in_background_process #407).
• Improves a handful of test timeouts.

[codecov-commenter]

Codecov Report

Merging #420 (68cff1e) into development (51587f9) will decrease coverage by 7.37%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development     #420      +/-   ##
===============================================
- Coverage        87.32%   79.95%   -7.38%     
===============================================
  Files              100      100              
  Lines             5737     5742       +5     
===============================================
- Hits              5010     4591     -419     
- Misses             727     1151     +424     

Impacted Files	Coverage Δ
compiler_gym/envs/compiler_env.py	84.69% <ø> (-3.83%)	⬇️
...er_gym/third_party/inst2vec/inst2vec_preprocess.py	10.76% <0.00%> (-63.47%)	⬇️
compiler_gym/envs/llvm/compute_observation.py	28.57% <0.00%> (-59.53%)	⬇️
compiler_gym/envs/llvm/datasets/clgen.py	40.67% <0.00%> (-50.85%)	⬇️
compiler_gym/envs/llvm/llvm_benchmark.py	42.17% <0.00%> (-45.86%)	⬇️
compiler_gym/third_party/inst2vec/__init__.py	56.66% <0.00%> (-36.67%)	⬇️
compiler_gym/envs/llvm/datasets/chstone.py	50.00% <0.00%> (-32.50%)	⬇️
compiler_gym/envs/llvm/datasets/csmith.py	55.88% <0.00%> (-32.36%)	⬇️
compiler_gym/envs/llvm/datasets/llvm_stress.py	65.51% <0.00%> (-31.04%)	⬇️
compiler_gym/spaces/reward.py	60.78% <0.00%> (-13.73%)	⬇️
... and 11 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 51587f9...68cff1e. Read the comment docs.