Use SciMLTesting v1.2 folder-based run_tests

Convert the test suite to SciMLTesting v1.2. JumpProcesses has GPU-only
groups (CUDA, Correctness) that are not declared in test_groups.toml and are
run by a separate GPU.yml workflow against the gpu/ sub-environment, so the
bare folder-discovery mode cannot express them. This uses the explicit-args
run_tests form over a folder layout instead.

Folder layout:
- test/InterfaceI/  : the 21 files GROUP=InterfaceI ran (top-level moves).
- test/InterfaceII/ : the 18 files GROUP=InterfaceII ran, including the
  former test/spatial/*.jl (flattened; each is self-contained).
- test/qa/qa.jl     : the QA body (runs in the root test env; Aqua +
  ExplicitImports live in the root [extras]).
- test/gpu/         : unchanged (CUDA env).
- test/shared/run_spatial_tests.jl : the unused manual spatial driver,
  parked out of the group folders (never run by runtests.jl).

runtests.jl becomes a single run_tests(...) call:
- groups = InterfaceI / InterfaceII / CUDA / Correctness thunks. The CUDA and
  Correctness thunks keep activate_gpu_env() verbatim.
- qa = test/qa/qa.jl.
- all = ["InterfaceI", "InterfaceII"] (curated; matches the old
  All = InterfaceI + InterfaceII, with QA/CUDA/Correctness excluded).
Each Interface thunk keeps the original @safetestset labels and run order,
only updating the include paths to the new folders.

The set of tests run under each GROUP value (All, InterfaceI, InterfaceII,
QA, CUDA, Correctness) is unchanged. test/test_groups.toml is untouched.

Deps: add SciMLTesting to root [extras]/[targets].test and [compat]. Pkg is
retained (activate_gpu_env still uses it). SafeTestsets/Test already present.

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

Author: ChrisRackauckas