compiler: one build_module/set_params path for all three module owners

Simulation, PeriodicBlockStepper and FixedPatchStepper levels each repeated
generate_config -> compile_kernel -> load_module -> cleanup and the
d_params pack/upload. They now call compiler.build_module(cfg, entry,
arch=..., n_objects=..., block_root_bc=...) and compiler.set_params.
Simulation no longer keeps its build directory alive until close (nothing
read it after loading). Removes the unused compile_kernel_v2 alias.
Host fakes and lifecycle tests follow the new seam; the close-retry case
for build-directory cleanup goes with the removed cleanup step.
No kernel, numerical or launch change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/test_refinement_three_level_multipatch.py

@@ -193,9 +193,9 @@ def mock_backend(*, children=CHILDREN, bodies=False, fail_compile=False, fail_up
         gpu.get_function.side_effect=lambda name: Mock(name=name)
         gpu.get_global.side_effect=lambda name: (Mock(),20 if name=='d_params' else 16)
         return gpu
-    module.compiler.load_module.side_effect=load
+    module.compiler.build_module.side_effect=lambda *a,**k: load(None)
     if fail_compile:
-        module.compiler.compile_kernel.side_effect=['first','second',RuntimeError('L2 compile failed')]
+        module.compiler.build_module.side_effect=[load(None),load(None),RuntimeError('L2 compile failed')]
     if fail_upload:
         def upload(*args):
             if len(allocations)>20: