Speedup execution of sqllogictests with more parallelization

[alamb]

Is your feature request related to a problem or challenge?

@blaginin is trying to speed up execution of tests

Right now, when running the tests by default it takes 8 wallclock seconds with 16 cores.

cargo test --profile=ci  --test sqllogictests
...
Running with 16 test threads (available parallelism: 16)
Completed 407 test files in 8 seconds

However, if you run time, you can see this only consumes 53 coresec out of a theoretical 128 coresec ( 16 cores * 8 seconds = 128 core*sec)

time cargo test --profile=ci  --test sqllogictests
    Finished `ci` profile [unoptimized] target(s) in 0.34s
     Running bin/sqllogictests.rs (target/ci/deps/sqllogictests-91ecf623e0e3b627)
Running with 16 test threads (available parallelism: 16)
Completed 407 test files in 8 seconds
real	0m8.232s
user	0m53.201s
sys	0m1.247s

This means the tests could in theory go twice as fast with more cores

I when looked briefly at this, I think one problem is that the push_down_filter.slt test takes a long time and is single threaded for that time

[00:00:05] ####################--------------------      52/107     "push_down_filter.slt" - 4 took > 500 ms

Describe the solution you'd like

I would like the sqllogictests to run on all cores

Describe alternatives you've considered

Maybe we can start by splitting up push_down_filter.slt into a few smaller files that can run in parallel

Additional context

No response