Configure density and gradient corrections independently

[svchb]

Summary

• add CorrectionConfiguration for independent density and gradient corrections
• add density_correction and gradient_correction keywords to WCSPH, EDAC, and dummy boundaries
• compose correction caches without duplicating lifecycle logic
• retain the existing correction keyword and reject ambiguous mixed configuration
• add metadata and explicit IISPH rejection
• move combined-configuration coverage into a dedicated test file

Stack

Depends on #1289 and therefore on the complete correction-method stack. This PR targets main and temporarily includes the preceding commits.

Review-only diff: svchb/TrixiParticles.jlOpen@fix/asymmetric-correction-pressure-conservation...feature/independent-correction-configuration

Isolated layer: 10 files, 194 additions, 13 deletions.

Verification

• complete unit suite passed
• JuliaFormatter and git diff --check passed

[codecov]

Codecov Report

❌ Patch coverage is 92.73859% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.64%. Comparing base (a720b1d) to head (16a6542).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
test/examples/gpu.jl	0.00%	23 Missing ⚠️
src/general/corrections.jl	89.28%	6 Missing ⚠️
src/io/io.jl	0.00%	5 Missing ⚠️
src/schemes/structure/rigid_body/system.jl	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1285      +/-   ##
==========================================
+ Coverage   90.39%   90.64%   +0.25%     
==========================================
  Files         138      146       +8     
  Lines       11322    11767     +445     
==========================================
+ Hits        10234    10666     +432     
- Misses       1088     1101      +13     

Flag	Coverage Δ
total	90.65% <92.73%> (+0.25%)	⬆️
unit	79.38% <92.73%> (+1.90%)	⬆️

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