[BugFix] Fix incremental detokenization perf issue

[njhill]

max was meant to be min - could cause O(n^2) blowup in pathological cases

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[WoosukKwon]

Where does 24 come from? Can we use smaller numbers like 5?

[njhill]

It's to try to find a small suffix to start from, or else it has to loop over the entire prompt below decoding the tokens one-by-one, which could be very long.

[WoosukKwon]

So, does it mean we can't use smaller numbers?

[WoosukKwon]

LGTM. Thanks for the fix! The performance looks normal after this PR:

============ Serving Benchmark Result ============
Successful requests:                     100       
Benchmark duration (s):                  45.27     
Total input tokens:                      1000000   
Total generated tokens:                  20000     
Request throughput (req/s):              2.21      
Output token throughput (tok/s):         441.79    
Total Token throughput (tok/s):          22531.15  
---------------Time to First Token----------------
Mean TTFT (ms):                          974.65    
Median TTFT (ms):                        413.66    
P99 TTFT (ms):                           2323.33   
-----Time per Output Token (excl. 1st token)------
Mean TPOT (ms):                          66.89     
Median TPOT (ms):                        77.80     
P99 TPOT (ms):                           83.48     
---------------Inter-token Latency----------------
Mean ITL (ms):                           66.89     
Median ITL (ms):                         27.12     
P99 ITL (ms):                            246.34    
==================================================