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_jets.py

@@ -16,7 +16,7 @@ from unittest.mock import Mock, patch
 import numpy as np
 import pycuda.driver as cuda
 
-from CelerisLab.cuda import compiler_v2 as compiler
+from CelerisLab.cuda import compiler
 from CelerisLab.lbm.descriptors import SOLID
 from CelerisLab.lbm.refinement import ACTIVE, FixedPatch2D, prepare_fine_boundary
 from CelerisLab.lbm.refinement_stepper import FixedPatchStepper