GH-421: Ensure temporary spaces and plugin scratches cannot collide

[ascopes]

• Temporary spaces are now scoped to the current goal and execution ID.
• JVM plugin hashes now include an increasing index to prevent duplicate plugins in the same execution overwriting the same files in the scratch space.

Fixes GH-421.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.71%. Comparing base (84ad167) to head (a06ac68).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #422      +/-   ##
==========================================
+ Coverage   87.65%   87.71%   +0.06%     
==========================================
  Files          33       33              
  Lines        1117     1122       +5     
  Branches       75       75              
==========================================
+ Hits          979      984       +5     
  Misses        104      104              
  Partials       34       34              

Files with missing lines	Coverage Δ
...protobufmavenplugin/generation/TemporarySpace.java	86.67% <100.00%> (+4.85%)	⬆️
...protobufmavenplugin/plugins/JvmPluginResolver.java	84.51% <100.00%> (+0.11%)	⬆️