GlobalDiffEq: add adjoint-based global error control as a SciMLSensitivity extension

[ChrisRackauckas-Claude]

Important

Ignore this PR until it has been reviewed by @ChrisRackauckas.

Now rebased onto master — #3929 (the repo transfer) has merged, so this PR is the base of the remaining GlobalDiffEq stack. The single commit here is the only change; review it directly.

Summary

Adds GlobalAdjoint and adjoint_error_estimate — adjoint-based a posteriori global error estimation and control (Cao and Petzold, SISC 26(2), 2004; closes SciML/GlobalDiffEq.jl#4). This is SciML/GlobalDiffEq.jl#56 carried into the monorepo, restructured as the package extension GlobalDiffEqSciMLSensitivityExt on SciMLSensitivity + QuadGK weakdeps so the base sublibrary stays light.

Differences from GlobalDiffEq.jl#56:

• The SciMLSensitivity/QuadGK-touching internals (ODEAdjointProblem construction, defect quadrature, the default sensealg) moved into the extension; the algorithm struct, validation, fixed-parameter SciMLStructures wrapper, orthogonal-direction sampling, and the gtol control loop stay in the package.
• sensealg defaults to nothing and resolves to SciMLSensitivity.QuadratureAdjoint(autojacvec = true) when the extension is loaded; solving without the extension raises an ArgumentError instructing to run using SciMLSensitivity, QuadGK.
• Otherwise the public API and semantics are identical, and the test suite is the same plus an invalid-sensealg constructor check.

Version 1.3.0 (new public API), matching the bump proposed in GlobalDiffEq.jl#56.

Validation (run locally)

• ODEDIFFEQ_TEST_GROUP=Core julia --project=lib/GlobalDiffEq -e 'using Pkg; Pkg.test()': pass — Basic 1/1, traits 3/3, Adjoint estimation and control 14/14, BigFloat 2/2
• ODEDIFFEQ_TEST_GROUP=QA julia --project=lib/GlobalDiffEq -e 'using Pkg; Pkg.test()': pass — 22 passed, 1 pre-existing declared broken
• The adjoint estimate/control tests verify the estimator against the analytic solution of a linear problem (ratio within 15%), gtol-controlled solves meeting a 1e-6 endpoint error, callable parameters, and the argument validation paths.

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https://claude.ai/code/session_01MfUh8tgp3iBmMv9nkBqoyY