Bump compat for OrdinaryDiffEq v7 / SciMLBase v3 ecosystem

[ChrisRackauckas-Claude]

Summary

Widens compat bounds and applies breaking-change migrations for the OrdinaryDiffEq v7 / SciMLBase v3 ecosystem release (SciML/OrdinaryDiffEq.jl#3562, cascade revert SciML/OrdinaryDiffEq.jl#3565).

See also: OrdinaryDiffEq NEWS.md

Compat bumps (docs/Project.toml)

Package	Old compat	New compat
OrdinaryDiffEq	"6"	"6, 7"
OrdinaryDiffEqRosenbrock	"1"	"1, 2"

Note: OrdinaryDiffEqCore was NOT bumped to v5 (that was reverted in #3565; v4 is current). DifferentialEquations compat remains at "7" (no new major there).

Source migrations applied

These are the only usages of breaking APIs found in the docs source:

• docs/src/showcase/optimization_under_uncertainty.md: Migrate ensemble prob_func(prob, i, repeat) → prob_func(prob, ctx) (new EnsembleProblem API in OrdinaryDiffEq v7 / SciMLBase v3).
• docs/src/showcase/massively_parallel_gpu.md: Same prob_func signature migration.
• docs/src/showcase/ode_types.md: Migrate sol[11] → sol.u[11] (RAT v4 element-first integer indexing change: sol[i] is now element-first, use sol.u[i] to access the state at the i-th saved timestep).

No destats/has_destats, DEAlgorithm, chunk_size/standardtag/diff_type/autodiff=Bool, or u_modified! usages were found in the docs source.

Test plan

• Confirm Pkg.instantiate() resolves with OrdinaryDiffEq v7 and OrdinaryDiffEqRosenbrock v2 in the docs environment
• CI docs build passes (primary signal)
• Check that tutorial examples using prob_func and sol[i] are syntactically valid with the new API

🤖 Generated with Claude Code

[ChrisRackauckas-Claude]

CI Notes

The `Build and Deploy Aggregate Documentation` job failed with:

ERROR: expected package `AdvancedHMC [0bf59076]` to be registered

This failure is unrelated to the compat changes in this PR. The error occurs in the `Pkg.develop` step on the self-hosted runner `demeter4-3`, which appears to have a stale Julia registry cache that doesn't contain `AdvancedHMC`. The previous run (at 00:34 UTC today) succeeded on runner `demeter4-1` with the same `AdvancedHMC = "0.8"` compat entry already in the `docs/Project.toml` prior to this PR.

The `AdvancedHMC` package IS present in the General registry (UUID 0bf59076) — this is a runner-infrastructure cache issue. Triggering a re-run should use a healthy runner.