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_block_step_sync.py

@@ -37,7 +37,7 @@ def backend():
     module.get_global.return_value = (Mock(), 20)
     module.get_function.side_effect = lambda name: Mock(
         side_effect=lambda *a, **k: log.append((name, a[:2])))
-    host.compiler.load_module.return_value = module
+    host.compiler.build_module.return_value = module
     cfg = LBMConfig(nx=16, ny=16, viscosity=.1)
     run = host.PeriodicBlockStepper(cfg, BlockLayout2D.build(16, 16, 8, 8),
                                     context=Mock(activate=nullcontext, sm_arch="sm_70"))