Make PST GPU-compatible

[efaulhaber]

As requested by @LasNikas.

[codecov]

Codecov Report

Attention: Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.

Project coverage is 70.74%. Comparing base (6d04215) to head (41b0096).
Report is 56 commits behind head on main.

Files with missing lines	Patch %	Lines
src/callbacks/particle_shifting.jl	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #813      +/-   ##
==========================================
+ Coverage   70.53%   70.74%   +0.21%     
==========================================
  Files          96      106      +10     
  Lines        5976     6710     +734     
==========================================
+ Hits         4215     4747     +532     
- Misses       1761     1963     +202     

Flag	Coverage Δ
unit	70.74% <54.54%> (+0.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull Request Overview

Aligns particle shifting and velocity extraction routines to be GPU-compatible by introducing specialized dispatch and buffer handling.

• Adds current_velocity overloads for GPU-friendly extraction based on density calculators.
• Refactors particle_shifting! to use a combined temp cache and replaces CPU-based max-velocity computation with a GPU-compatible approach.
• Adjusts the literal for R to a rational form.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/schemes/fluid/weakly_compressible_sph/system.jl	Added current_velocity methods for SummationDensity and ContinuityDensity
src/callbacks/particle_shifting.jl	Renamed temp cache to vu_cache, replaced eachparticle max with reinterpret approach, and changed R literal

Comments suppressed due to low confidence (2)

src/schemes/fluid/weakly_compressible_sph/system.jl:254

• [nitpick] Consider adding unit tests for both SummationDensity and ContinuityDensity cases of current_velocity to verify GPU-compatible behavior under different density calculators.

@inline function current_velocity(v, ::SummationDensity,

src/callbacks/particle_shifting.jl:68

• SVector is used here but not imported in this file; add using StaticArrays: SVector at the top to prevent an undefined constant error.

reinterpret(reshape, SVector{ndims(system), eltype(v)},

[LasNikas]

\run-gpu-tests

[svchb]

/run-gpu-tests