Conserve corrected pressure pair momentum

[svchb]

Summary

• add conservative asymmetric pressure formulations using both corrected pair gradients
• make EDAC average-pressure reduction pair symmetric
• reconstruct the fluid-oriented pressure force and apply its exact structure reaction
• preserve WCSPH free-surface pressure correction in the reaction path
• add algebraic, full-RHS, rigid-body, and TLSPH conservation tests

Stack

Depends on #1288. This PR targets main and temporarily includes the preceding stack.

Review-only diff: svchb/TrixiParticles.jlOpen@fix/mixed-kernel-gradient-correction...fix/asymmetric-correction-pressure-conservation

Isolated layer: 12 files, 450 additions, 22 deletions.

Verification

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

[codecov]

Codecov Report

❌ Patch coverage is 93.48315% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.66%. Comparing base (a720b1d) to head (9328f85).
⚠️ 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	85.71%	5 Missing ⚠️
src/schemes/structure/rigid_body/system.jl	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1289      +/-   ##
==========================================
+ Coverage   90.39%   90.66%   +0.27%     
==========================================
  Files         138      145       +7     
  Lines       11322    11730     +408     
==========================================
+ Hits        10234    10635     +401     
- Misses       1088     1095       +7     

Flag	Coverage Δ
total	90.67% <93.48%> (+0.27%)	⬆️
unit	79.33% <93.48%> (+1.85%)	⬆️

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