async test hangs on vps with two cores

[blnote]

After observing sporadic concurrency errors when querying a Datalog DB, I noticed that running lein test on the current Datalevin repo hangs on datalevin.async-test.

my environment:

shared virtual cpu with 2 cores (intel xeon gold), 4GB RAM
openjdk 21.0.7 2025-04-15
OpenJDK Runtime Environment (build 21.0.7+6-Ubuntu-0ubuntu124.04)
OpenJDK 64-Bit Server VM (build 21.0.7+6-Ubuntu-0ubuntu124.04, mixed mode, sharing)

there was no problem with the async test on laptop with 4 cores (Intel(R) Core(TM) i5-8350U CPU)