Fix v7: second eachindex(sol2) in dense_tests, EEst access in TSRKC3 (#3457)

- test/regression/ode_dense_tests.jl line 69: second `eachindex(sol2)`
  instance (1D linear problem loop) that was missed by #3446. Same RAT v4
  issue — `eachindex(sol)` now returns CartesianIndices, use
  `eachindex(sol2.u)` for the per-timestep iteration.

- lib/OrdinaryDiffEqStabilizedRK/src/rkc_perform_step.jl lines 1191 and
  1323: `integrator.EEst = ...` throws `FieldError` since #3422 moved
  EEst from the integrator struct to the controller cache. Replace with
  `OrdinaryDiffEqCore.set_EEst!(integrator, ...)` matching every other
  sublibrary.

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

lib/OrdinaryDiffEqStabilizedRK/src/rkc_perform_step.jl

@@ -1188,7 +1188,7 @@ end
             tmp, uprev, u, integrator.opts.abstol,
             integrator.opts.reltol, integrator.opts.internalnorm, t
         )
-        integrator.EEst = integrator.opts.internalnorm(atmp, t)
+        OrdinaryDiffEqCore.set_EEst!(integrator, integrator.opts.internalnorm(atmp, t))
     end
     integrator.k[1] = integrator.fsalfirst
     integrator.k[2] = integrator.fsallast
@@ -1320,7 +1320,7 @@ end
             atmp, tmp, uprev, u, integrator.opts.abstol,
             integrator.opts.reltol, integrator.opts.internalnorm, t
         )
-        integrator.EEst = integrator.opts.internalnorm(atmp, t)
+        OrdinaryDiffEqCore.set_EEst!(integrator, integrator.opts.internalnorm(atmp, t))
     end
     integrator.k[1] = integrator.fsalfirst
     integrator.k[2] = integrator.fsallast

test/regression/ode_dense_tests.jl

@@ -66,7 +66,7 @@ function regression_test(
     @inferred sol(interpolation_results_1d, interpolation_points)
     @inferred sol(interpolation_points[1])
     sol2 = solve(prob_ode_linear, alg, dt = 1 // 2^(4), dense = true, adaptive = false)
-    for i in eachindex(sol2)
+    for i in eachindex(sol2.u)
         print_results(
             @test maximum(abs.(sol2.u[i] - interpolation_results_1d[i])) <
                 tol_ode_linear