Downgrade: raise SciMLBase floor to 3 (LTS precompile method collision with SciMLBase 2.x)

[ChrisRackauckas-Claude]

Problem

The Downgrade workflow (Julia 1.10, the LTS floor) failed. The latest failing run
reported an Unsatisfiable on OrdinaryDiffEq in the 06-10 log, but after the recent
registry changes the resolve itself now succeeds — and the downgrade is currently red for
a deeper reason that the old floors were masking.

The compat declared SciMLBase = "2.152, 3", so the downgrade pins SciMLBase to its
floor in the 2.x range. SciMLBase 2.x still defines
RecursiveArrayTools.tuples(::DEIntegrator) and tuples(::AbstractTimeseriesSolution)
(in its integrator/solution interface). SciMLIterators does import RecursiveArrayTools: tuples
and redefines those exact methods (the utilities were extracted out of SciMLBase into
this package). At SciMLBase 2.x this is a method overwrite, which is fatal during module
precompilation on Julia 1.10:

WARNING: Method definition tuples(SciMLBase.DEIntegrator...) in module SciMLBase ...
         overwritten in module SciMLIterators ...
ERROR: Method overwriting is not permitted during Module precompilation.

The half-precompiled module then drops later-defined exports, so the test suite fails with
UndefVarError: TimeChoiceIterator not defined.

SciMLBase 3.x removed those tuples(::DEIntegrator / ::AbstractTimeseriesSolution)
definitions, so there is no collision — at latest versions SciMLIterators precompiles and
tests pass (including on Julia 1.10). SciMLIterators' source therefore genuinely requires
SciMLBase 3.

Fix

Raise the floors to the SciMLBase-3-only minimums:

• SciMLBase = "3" (2.x is incompatible with this package's source)
• OrdinaryDiffEq = "7" (OrdinaryDiffEq 7 ⟺ SciMLBase 3; OrdinaryDiffEq 6 pairs with SciMLBase 2 and is uninstallable here)
• RecursiveArrayTools = "4" (OrdinaryDiffEq 7 requires RecursiveArrayTools 4.x; the old "3" floor is unreachable)

No upper bound is touched. Each new floor is a real minimum: the lower versions are
genuinely uninstallable for a SciMLBase-3-only package.

Verification

Ran the actual julia-actions/julia-downgrade-compat (Resolver.jl --min=@deps) on
Julia 1.10 (the LTS downgrade floor):

• The merged test env resolves to SciMLBase 3.0.0, OrdinaryDiffEq 7.0.0, RecursiveArrayTools 4.0.0.
• Pkg.test on that downgraded environment passes ("Testing SciMLIterators tests passed").
• Previously (with the 2.152 floor allowing SciMLBase 2.152.0) the same Pkg.test errored
  with the precompile method overwrite → UndefVarError: TimeChoiceIterator not defined.

Note: SciMLBase still defining these tuples methods in the 2.x series (which SciMLIterators
re-defines) is the underlying source-level collision; raising the floor to SciMLBase 3 sidesteps
it because 3.x no longer defines them.

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This PR should be ignored until reviewed by @ChrisRackauckas.

🤖 Generated with Claude Code