[Hopper CuTeDSL] Add FP8 GEMM with 2xAcc (#3149)

Add dense_gemm_fp8_2xacc.py — a CuTeDSL port of CUTLASS Example 54
(54_hopper_fp8_warp_specialized_gemm.cu) for NVIDIA Hopper (SM90).

Implements D = scale_a * scale_b * (A @ B) where A/B are FP8 E4M3FN using
the 2xAcc (double accumulation) technique: a temporary accumulator is
periodically promoted into the main accumulator every mma_promotion_interval
MMA instructions to prevent FP8 precision loss.

Features:
- FP8 E4M3FN inputs with Float32 accumulation
- 2xAcc for improved numerical accuracy
- TMA with multicast for A/B/D transfers
- WGMMA warp-specialized persistent tile scheduling
- Configurable output dtype: Float16, Float32, Float8E4M3FN
- Scalar scale_a / scale_b epilogue factors
- Cluster shapes up to 2x2

Add pytest test suite covering:
- L0 compile tests: all tile shapes, cluster shapes, output dtypes,
  mma_promotion_interval values
- L1 correctness tests: numerical validation vs torch.einsum reference
  for all configs, non-trivial scale factors, and batched GEMM (L>1)
- Benchmark tests (pytest -m bench -s): representative problem sizes
  with warmup, cold-L2, and TFLOPS reporting

Also fix conftest.py to import cutlass before adding examples/python/CuTeDSL
to sys.path, preventing the jax/ examples subdirectory from being detected
as a namespace package and breaking cutlass's JAX availability check.

test/examples/CuTeDSL/conftest.py

@@ -41,6 +41,15 @@ import numpy as np
 project_root = Path(__file__).resolve().parent.parent.parent.parent
 example_path = project_root / "examples" / "python" / "CuTeDSL"
 utils_path = project_root / "test" / "utils"
+
+# Import cutlass *before* adding example_path to sys.path.
+# The examples directory contains a `jax/` subdirectory that Python 3 treats
+# as a namespace package.  If that directory is on sys.path first, cutlass's
+# JAX-availability check (which does a bare `import jax`) incorrectly returns
+# True, and the subsequent `import jax.numpy` fails with ModuleNotFoundError.
+# Importing cutlass here, while sys.path is still clean, avoids that race.
+import cutlass  # noqa: E402  (intentional early import)
+
 sys.path.append(str(example_path))
 sys.path.append(str(utils_path))