SNOW-2380741: Use all logical cores in snowpark tests.

[sfc-gh-mvashishtha]

Formerly, we had limited the test parallelism to not overwhelm our Snowflake deployments, but now that we are using multi-cluster warehouses, we should be able to use all 64 cores.

This change speeds up Modin CI jobs according to a sample size of 1. Other long-running CI jobs seem to take about as long before and after. before vs after:

test	before (minutes)	after (minutes)
modin-macos-latest-3.9-aws	30	28
modin-ubuntu-latest-64-cores-3.10-azure	42	31
modin-ubuntu-latest-64-cores-3.12-aws	48	30
modin-windows-latest-64-cores-3.11-gcp	71	42

[sfc-gh-joshi]

Is it possible to use pytest -n auto instead in case we change CI runners in the future?

[sfc-gh-mvashishtha]

Is it possible to use pytest -n auto instead in case we change CI runners in the future?

Done.

[sfc-gh-mvashishtha]

I'm marking this PR as a draft because:

• it may cause OOMs for AST tests
• I think we can go even faster with -n 128 since modin tests are network-bound.

[sfc-gh-mvashishtha]

I found that using 128 cores seemed to push the GitHub Actions runners beyond their capacity so that they failed with exit code 143: #3824

I used the previous level of parallelism for AST tests, which seem to use too many resources when we use -n logical.