feat(kda): add KDA (Kimi Delta Attention) kernels, backend, and tests (#1051)

- Add KDA Pallas kernel (python/sgl_jax/srt/kernels/kda/) with naive reference
- Add KDA attention backend (linear/kda_backend.py) and short convolution layer
- Wire KDA into hybrid_linear_attn_backend and radix_linear_attention
- Add unit tests for TP and DP paths (test_kda_attention*.py, test_short_conv.py)
- Register tests in unit-test-tpu-v6e-4 suite

Author: MokusMokun

python/sgl_jax/srt/kernels/kda/__init__.py

@@ -0,0 +1,4 @@
+from sgl_jax.srt.kernels.kda.kda import chunk_kda_fwd as chunk_kda
+from sgl_jax.srt.kernels.kda.naive import naive_recurrent_kda
+
+__all__ = ["chunk_kda", "naive_recurrent_kda"]