workload: ycsb-e creates a single hot range

[kvoli]

Describe the problem

Running the YCSB-E workload, one range has 99% of the request load and remains above the split threshold, despite not splitting.

The range appears to have sufficient rows to split:

 /Table/106/1 to /Max

This causes a hotspot to develop on the leaseholder for this range. Which does not dissipate.

To Reproduce

export gce_project=cockroach-ephemeral
export email=austen-ycsbe
roachprod create $email -n 8 --gce-machine-type=n1-standard-16

# recent commit on master
roachprod stage $email cockroach 4f0065ad010cee1ce50bbc65019b26f93a7dc6ad
roachprod start $email:1-7

# stimulate some rebalancing activity
roachprod run $email:8 -- './cockroach workload init ycsb --workload E --drop {pgurl:1-7}'
roachprod run $email:8 -- './cockroach workload run ycsb --max-rate 50000 --workload E {pgurl:1-7}'

Jira issue: CRDB-19250

[kvoli]

observability to diagnose this issue #87276