Update tokenizers submodule to the linear-time HF encode path

Bump extension/llm/tokenizers, picking up the linear-time
HFTokenizer encode work (merge_all O(n log n), ReplaceNormalizer::normalize
O(N) single forward pass) plus a targeted encode-latency benchmark. This cuts
long-prompt prefill tokenization time in the gemma4 / eagle3 runners; token ids
and greedy output are unchanged, verified e2e on the gemma4-31B target
(identical 18-token encode + decode after the bump).

ghstack-source-id: 525dc35
ghstack-comment-id: 4734208425
Pull-Request: #20349

Author: digantdesai