CompatHelper: bump compat for SciMLBase to 3, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the SciMLBase package from 2 to 2, 3.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.71%. Comparing base (2277802) to head (ef14ed7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1134      +/-   ##
==========================================
- Coverage   88.72%   88.71%   -0.02%     
==========================================
  Files         128      128              
  Lines        9745     9745              
==========================================
- Hits         8646     8645       -1     
- Misses       1099     1100       +1     

Flag	Coverage Δ
total	88.71% <ø> (-0.02%)	⬇️
unit	66.98% <ø> (ø)

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[svchb]

Looking at the changelog https://github.com/SciML/SciMLBase.jl/releases/tag/v3.0.0 there are several changes that actually require fixing for v3

Test only pass because there is a version conflict with something else and we don't get V3 in the test runs.

[ChrisRackauckas-Claude]

Courtesy note from the SciMLBase v3 ecosystem sweep: this compat bump has a non-trivial v3 surface area to check before merging.

14 u_modified! call sites in src/, with the package importing u_modified! directly from SciMLBase at src/TrixiParticles.jl:26. Hottest sites:

• src/preprocessing/particle_packing/system.jl:275, :382
• src/schemes/boundary/open_boundary/system.jl:345
• src/schemes/fluid/shifting_techniques.jl:514
• src/callbacks/sorting.jl:97

SciMLBase v3 renamed u_modified! → derivative_discontinuity! with an @deprecate shim, so existing calls still work but emit deprecation warnings.

Suggested pattern (matches SciML/DiffEqCallbacks.jl#300):

@static if isdefined(SciMLBase, :derivative_discontinuity!)
    using SciMLBase: derivative_discontinuity!
else
    const derivative_discontinuity! = SciMLBase.u_modified!
end

That replaces the direct using SciMLBase: u_modified! at src/TrixiParticles.jl:26 and lets the file load cleanly under both SciMLBase v2 and v3 without a minimum-version bump. The 14 call sites then just need a find-and-replace from u_modified! to derivative_discontinuity!.

Resolution caveat: CI will currently fail at Pkg.add on any env pulling SciMLBase 3.1 because OrdinaryDiffEq still pins RecursiveArrayTools ≤ 3.54. This will self-resolve once OrdinaryDiffEq bumps.

Other v3 flags in src/test came up clean: no DEProblem refs, no 3-arg ensemble prob_func, no single-int timeseries sol[i] indexing.

cc @ChrisRackauckas