cuda: compiler_v2 module becomes compiler

The package already exposed it as CelerisLab.cuda.compiler; the module now
has that name and every tip caller, doc and current-tree test imports it
directly (no alias).

Historical-revision tooling is not edited: the Taylor-Green harness
(run_case.py, hash-pinned check_projected_pairs.py, assess receipts) only
runs against a135252, whose package has cuda/compiler_v2.py, and the J
campaign runners and dated docs describe past trees. Its two current-tree
tests now import that package from git (historical_package) instead of the
tip, and the kernel-root test first checks the accepted case.

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

tests/validation/multigrid/test_refinement_gpu.py

@@ -20,7 +20,7 @@ import pycuda.driver as cuda
 
 import CelerisLab
 from CelerisLab.config import LBMConfig
-from CelerisLab.cuda import compiler_v2 as compiler
+from CelerisLab.cuda import compiler
 from CelerisLab.cuda.context import CudaContext
 from CelerisLab.lbm.refinement_stepper import FixedPatchStepper, PeriodicPatchStepper