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_step_sync.py

@@ -31,7 +31,7 @@ def backend(window=False):
     module.get_global.return_value = (Mock(), 20)
     module.get_function.side_effect = lambda name: Mock(
         side_effect=lambda *a, **k: log.append((name, a, k)))
-    host.compiler.load_module.return_value = module
+    host.compiler.build_module.return_value = module
     host.cuda.mem_alloc.side_effect = allocate
     host.cuda.memcpy_dtoh.side_effect = lambda array, pointer: array.fill(0)
     host.cuda.memset_d8_async.side_effect = lambda *a: log.append(("memset", a, {}))