[Fix] Write the req_to_token page tail so rows stay valid over whole pages

[hnyls2002]

The paged allocator hands out whole pages, but the row write only covers the requested tokens, so req_to_token[:, seq_len : ceil(seq_len)] keeps the previous occupant's indices. Fill that tail (slots inside a page are consecutive) and widen the row headroom to page_size - 1 for every page_size > 1 config, not just speculative ones.

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CI States

Latest PR Test (Base): ❌ Run #32304945912
Latest PR Test (Extra): ❌ Run #32304945576
Latest PR Test (AMD ROCm 10): ❌ Run #32304945813

[hnyls2002]

/rerun-test test_page_tail_indices.py test_dllm_fdfo_kv_reuse.py test_unified_radix_cache_kl_full.py test_streaming_session_swa.py

[github-actions]

Results for /rerun-test test_page_tail_indices.py test_dllm_fdfo_kv_reuse.py test_unified_radix_cache_kl_full.py test_streaming_session_swa.py:

🚀 ubuntu-latest (2 tests): ✅ View workflow run

cd test/ && python3 registered/unit/mem_cache/test_page_tail_indices.py
cd test/ && python3 registered/unit/mem_cache/test_dllm_fdfo_kv_reuse.py

🚀 2-gpu-h100 (1 test): ✅ View workflow run

cd test/ && python3 registered/radix_cache/unified_radix_tree/test_unified_radix_cache_kl_full.py

🚀 1-gpu-h100 (1 test): ✅ View workflow run

cd test/ && python3 registered/sessions/test_streaming_session_swa.py

[hnyls2002]

/tag-and-rerun-ci

[hnyls2002]

/rerun-test test_page_tail_indices.py test_hisparse_allocator.py test_disaggregation_hisparse.py test_disaggregation_decode_radix_cache.py test/registered/disaggregation/test_disaggregation_basic.py

[github-actions]

Results for /rerun-test test_page_tail_indices.py test_hisparse_allocator.py test_disaggregation_hisparse.py test_disaggregation_decode_radix_cache.py test/registered/disaggregation/test_disaggregation_basic.py:

🚀 ubuntu-latest (2 tests): ✅ View workflow run

cd test/ && python3 registered/unit/mem_cache/test_page_tail_indices.py
cd test/ && python3 registered/unit/mem_cache/test_hisparse_allocator.py

🚀 8-gpu-h200 (1 test): ✅ View workflow run

cd test/ && python3 registered/disaggregation/test_disaggregation_hisparse.py

🚀 8-gpu-h20 (1 test): ✅ View workflow run

cd test/ && python3 registered/disaggregation/test_disaggregation_decode_radix_cache.py

🚀 2-gpu-h100 (1 test): ✅ View workflow run

cd test/ && python3 registered/disaggregation/test_disaggregation_basic.py

[hnyls2002]

/rerun-test test_page_tail_indices.py test_streaming_session_swa.py test_unified_radix_cache_kl_full.py test/registered/disaggregation/test_disaggregation_basic.py test_disaggregation_hisparse.py

[github-actions]

Results for /rerun-test test_page_tail_indices.py test_streaming_session_swa.py test_unified_radix_cache_kl_full.py test/registered/disaggregation/test_disaggregation_basic.py test_disaggregation_hisparse.py:

🚀 ubuntu-latest (1 test): ✅ View workflow run

cd test/ && python3 registered/unit/mem_cache/test_page_tail_indices.py

🚀 1-gpu-h100 (1 test): ✅ View workflow run

cd test/ && python3 registered/sessions/test_streaming_session_swa.py

🚀 2-gpu-h100 (2 tests): ✅ View workflow run

cd test/ && python3 registered/radix_cache/unified_radix_tree/test_unified_radix_cache_kl_full.py
cd test/ && python3 registered/disaggregation/test_disaggregation_basic.py

🚀 8-gpu-h200 (1 test): ❌ View workflow run

cd test/ && python3 registered/disaggregation/test_disaggregation_hisparse.py

[hnyls2002]

/tag-and-rerun-ci