Implement JctExtension JUnit extension.

[ascopes]

This enables declaring workspaces on a class level as fields and annotating them with the 'Managed' annotation to enable automatic creation and closure of workspaces as part of the JUnit workflow, leading to cleaner declarative test code.

[github-actions]

Test Results

  2 177 files  +108    2 177 suites  +108   2s ⏱️ ±0s
27 548 tests +288  27 319 ✔️ +132  229 💤 +156  0 ❌ ±0 
27 822 runs  +288  27 593 ✔️ +132  229 💤 +156  0 ❌ ±0 

Results for commit f97da65. ± Comparison against base commit 6a55b8a.

[codecov-commenter]

Codecov Report

Merging #392 (f97da65) into main (7dc3570) will increase coverage by 0.40%.
The diff coverage is 90.66%.

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@@            Coverage Diff             @@
##             main     #392      +/-   ##
==========================================
+ Coverage   81.52%   81.92%   +0.40%     
==========================================
  Files          93       94       +1     
  Lines        2841     2904      +63     
  Branches      234      242       +8     
==========================================
+ Hits         2316     2379      +63     
  Misses        473      473              
  Partials       52       52              

Impacted Files	Coverage Δ
...va/io/github/ascopes/jct/workspaces/Workspace.java	100.00% <ø> (ø)
...hub/ascopes/jct/workspaces/impl/WorkspaceImpl.java	37.93% <53.33%> (+2.21%)	⬆️
...java/io/github/ascopes/jct/junit/JctExtension.java	100.00% <100.00%> (ø)