File manager implementation tests, simplify OutputContainerGroup expectations

[ascopes]

Closes #219.

• Implements file manager implementation tests
• OutputContainerGroup getFileForInput / getFileForOutput / getJavaFileForInput / getJavaFileForOutput
  methods will now only consider non-module container groups. Module containers
  should be inspected by calling .getModule("module.name").getFileForInput
  instead.

[github-actions]

Test Results

  1 544 files  +   181    1 544 suites  +181   0s ⏱️ ±0s
21 276 tests +1 096  21 264 ✔️ +1 096  12 💤 ±0  0 ❌ ±0 
21 540 runs  +1 096  21 528 ✔️ +1 096  12 💤 ±0  0 ❌ ±0 

Results for commit 5b3c9c2. ± Comparison against base commit 81bcc0f.

[codecov-commenter]

Codecov Report

Merging #321 (5b3c9c2) into main (81bcc0f) will increase coverage by 3.50%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main     #321      +/-   ##
==========================================
+ Coverage   75.35%   78.86%   +3.50%     
==========================================
  Files          90       90              
  Lines        2735     2697      -38     
  Branches      237      225      -12     
==========================================
+ Hits         2061     2127      +66     
+ Misses        600      514      -86     
+ Partials       74       56      -18     

Impacted Files	Coverage Δ
.../jct/containers/impl/OutputContainerGroupImpl.java	50.00% <ø> (+17.94%)	⬆️
.../containers/impl/ContainerGroupRepositoryImpl.java	57.57% <100.00%> (ø)
...opes/jct/filemanagers/impl/JctFileManagerImpl.java	100.00% <100.00%> (+56.34%)	⬆️