[TokenspeedMLA] Test causal multi-token DCP contract

TokenSpeed MLA 0.1.8 already derives each query token causal key bound from the per-request bound, query length, DCP rank, and token index. Keep the grouped batch/query/head wrapper contract and cover the previously missing causal, DCP, multi-token case.

Co-authored-by: OpenAI Codex <noreply@openai.com>

Author: 2 people

tests/v1/attention/test_mla_backends.py

@@ -844,6 +844,7 @@ def test_tokenspeed_mla_noncausal_capability():
     ("causal", "tokens_per_decode", "dcp_world_size", "dcp_rank"),
     [
         pytest.param(True, 1, 2, 1, id="causal-dcp"),
+        pytest.param(True, 3, 2, 1, id="causal-dcp-multi-token"),
         pytest.param(False, 3, 1, 0, id="noncausal-multi-token"),
     ],
 )