Downgrade: raise SciMLBase compat floor to 2.49 (old 2.0.0 floor unresolvable at downgrade minimum) (#87)

At the downgrade minimum, SciMLBase is pinned to its compat floor 2.0.0
(from `SciMLBase = "2, 3.1"`). The test target pulls in the full OrdinaryDiffEq
/ MethodOfLines / ModelingToolkit stack, which (unpinned) resolves to a recent
DiffEqBase. Modern DiffEqBase declares `SciMLBase` lower bounds well above
2.0.0 (e.g. DiffEqBase 6.130.1+ needs SciMLBase 2.0.1+, and the resolved stack
needs higher still), and OrdinaryDiffEqSDIRK at the resolved version has no
SciMLBase 2.0.x in range. So SciMLBase 2.0.0 has an empty intersection with the
co-installed solver stack -> Unsatisfiable for DiffEqBase / OrdinaryDiffEqSDIRK.

2.49.0 is the smallest SciMLBase that resolves with the current solver stack on
the LTS (1.10) downgrade floor (2.48.x and below remain unsatisfiable). The 3.1
upper series is unchanged; no upper bound lowered, no test logic touched.

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

Project.toml

@@ -13,7 +13,7 @@ SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 CommonSolve = "0.2"
 ExplicitImports = "1"
 PrecompileTools = "1"
-SciMLBase = "2, 3.1"
+SciMLBase = "2.49, 3.1"
 Test = "1"
 julia = "1.10"