docs(bpe): cite Incremental BPE Tokenization paper

Add a reference to Jiang and Gong, "Incremental BPE Tokenization"
(ICML 2026), in the tokenizer comparison section of the bpe README,
linking to the paper's full runtime analysis and the authors'
implementation at ModelTC/mtc-inc-bpe.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: gorzell

crates/bpe/README.md

@@ -300,3 +300,6 @@ This case is particularly challenging for tiktoken, which shows a quadratic grow
 The Huggingface encoder scales better, but becomes slower and slower compared to our implementation as input size increases.
 
 ![worst-case encoding runtime comparison](./images/performance-worstcase.svg)
+
+For a full runtime analysis of incremental BPE tokenization, see Jiang and Gong, ["Incremental BPE Tokenization"](https://arxiv.org/abs/2605.30813) (ICML 2026), which presents an algorithm with a worst-case $\mathcal{O}(n \log^2 t)$ complexity (where $n$ is the input length and $t$ is the maximum token length).
+Their implementation is available at [ModelTC/mtc-inc-bpe](https://github.com/ModelTC/mtc-inc-bpe).