fix(downgrade): add [sources] for sibling submodules and raise floors

The downgrade CI resolves each workspace submodule in isolation via
julia-downgrade-compat, which cannot resolve sibling submodule deps
(DiscreteMeasures, CanonicalMoments) since they are unregistered
path deps -> "unknown package UUID". Declare them via [sources] so the
action removes them for resolution and re-adds them to the manifest as
path deps (the same mechanism SciML tests.yml@v1 relies on).

Submodule floor bumps (verified resolvable + test-passing at floors on
Julia 1.10, deps-mode, allow_reresolve=true):

CanonicalMoments:
- add [sources] DiscreteMeasures = ../DiscreteMeasures.jl
- Polynomials: (none) -> "4"  (0.5.0 lacked AbstractPolynomial export)
- RecurrenceRelationships: (none) -> "0.2"
- add julia/LinearAlgebra/Statistics/DiscreteMeasures floors

OUQBase:
- add [sources] CanonicalMoments + DiscreteMeasures path deps
- SciMLBase: 2.89.1 -> 2.153  (2.89.1 held Optimization to 3.25.1, too
  old for the test stack's OptimizationBBO -> UndefVarError deduce_retcode;
  2.153 lets OptimizationBBO/OptimizationBase/Optimization resolve
  consistently, matching the passing latest-CI set)

Downgrade suite run locally at these floors: PASS
- CanonicalMoments: Orthogonal Polynomial Roots 11/11, Moment Sequence 260/260
- OUQBase: FloodProblem solve pipeline completes (was failing on deduce_retcode)

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

CanonicalMoments.jl/Project.toml

@@ -24,6 +24,15 @@ IntervalArithmeticExt = "IntervalArithmetic"
 SymbolicsExt = "Symbolics"
 
 [compat]
+julia = "1.10"
+DiscreteMeasures = "0.1"
+LinearAlgebra = "1.10"
+Polynomials = "4"
+RecurrenceRelationships = "0.2"
+Statistics = "1.10"
 IntervalArithmetic = "0.18 - 0.20, =0.20.9"
 Reexport = "1.2.2"
 Symbolics = "6.29.2"
+
+[sources]
+DiscreteMeasures = { path = "../DiscreteMeasures.jl" }

OUQBase.jl/Project.toml

@@ -27,8 +27,12 @@ NaNMath = "1.1.3"
 OrderedCollections = "1.7.0"
 Polynomials = "4.0.13"
 Reexport = "1.2.2"
-SciMLBase = "2.89.1"
+SciMLBase = "2.153"
 Symbolics = "6.39.1"
 
+[sources]
+CanonicalMoments = { path = "../CanonicalMoments.jl" }
+DiscreteMeasures = { path = "../DiscreteMeasures.jl" }
+
 [workspace]
 projects = ["test"]