[ChrisRackauckas-Claude]

Please ignore this PR until it has been reviewed by @ChrisRackauckas.

What changed and why

Pure [compat] lower-bound bump in lib/SciCompDSL/Project.toml extras:

• ModelingToolkit = "11" → "11.21"

No solver code, tests, or package versions were changed. Parent / ModelingToolkitBase floors from #4964 are untouched.

ModelingToolkit is a SciCompDSL test extra. The declared 11.x floor of 11 allows 11.0.0, which fails to precompile on Julia 1.10 (UndefVarError: ispublic not defined). 11.21.0 is the first 11.x floor verified to precompile on Julia 1.10.

Verification (Julia 1.10.11)

Pkg.develop of SciCompDSL, then Pkg.add(name="ModelingToolkit", version=...):

# 11.0.0 (old 11.x floor)
RESOLVE_OK ModelingToolkit 11.0.0

Same 11.0.0 then fails to precompile (isolated and via MathML extras, same package):

PRECOMPILE_FAIL
ERROR: LoadError: UndefVarError: `ispublic` not defined
  @ ModelingToolkit src/ModelingToolkit.jl (@import_mtkbase)

# 11.21.0 (new 11.x floor)
RESOLVE_OK ModelingToolkit 11.21.0
PRECOMPILE_OK ModelingToolkit 11.21.0

What was not verified

• Full SciCompDSL / parent test suite under the new floor (only develop + add + precompile).
• GPU, Downstream, Julia pre.

Links

• Same 11.0.0 ispublic floor: Raise ModelingToolkit test floor to 11.21 MathML.jl#120
• Same 11.21 load floor: Raise ModelingToolkit 11.x floor to 11.21 CatalystNetworkAnalysis.jl#82
• Already-merged parent LS/DiffEqBase floors: Raise LinearSolve and DiffEqBase downgrade floors #4964