Move the top-level test files that mirror no source file

[michakraus]

What

The test files at the top level of test/ that mirror no source file move to where the test convention puts them: test/<path>.jl for a test of src/<path>.jl, the directory of the sources for a test of several files of one directory, and test/integration/ for a test of the whole package. Each file keeps its label and group; only its path in test/runtests.jl changes.

old path	new path	source files the test reaches
test/defects.jl	test/integration/defects.jl	src/particle_list.jl, src/particle.jl, src/hdf5_utils.jl

Checks

• The layout check of the test convention: clean.
• run-tests.jl list on this branch and on main: labels and groups equal line for line; only the paths of the moved files differ.
• run-tests.jl full --jobs 4 on this branch and on main: both pass with the same totals over all files. Each moved file, run alone on main at its old path and here at its new path, gives the same totals for its label (selected (defects.jl -> integration/defects.jl): Pass 12 Fail 0 Error 0 Broken 0 Total 12).
• Julia julia version 1.13.1, load average At start: load averages 3,58 4,60 4,38. The base run started at 4.79 4.82 4.46 and the branch run at 6.25 5.15 4.59..
• Changed include paths or comments in the moved files: test/integration/defects.jl: none (the file has no relative include or joinpath(@__DIR__, ...) path).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.71%. Comparing base (4beb80c) to head (e89e265).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #19   +/-   ##
=======================================
  Coverage   85.71%   85.71%           
=======================================
  Files           3        3           
  Lines          98       98           
=======================================
  Hits           84       84           
  Misses         14       14           

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