Test parallel test actions

[sovdeeth]

Problem

tests take a significant amount of time when run sequentially.

Test duration: 30 seconds setup + 1 min for each environment
1 env 1:30
2 env 2:30
3 env 3:30
6 env 6:30

Solution

experiments shown here:

1. parallel modifier for tests. Runs multiple testing servers on the same machine using the same build of skript. Fast on machines with threads to spare. No benefit on github actions machines
2. customTest task that can run specific environments/junit/etc based on properties passed in through command line
3. automatic github load balancing. splits tests evenly into N parallel jobs. Kind of messy in the checks panel but fast.

We will be dropping 1.20.4 and 1.20.6 for 2.14, though, which would remove the need for Java 17 tests.

Testing Completed

Supporting Information

This is more a proof of concept + way to ask for opinions on different ideas. Please feel free to comment on these changes.

If there is interest in some of the above experiments, I'll make a proper pr for each one.

---

Completes: none
Related: none

[sovdeeth]

2 parallel tasks, with java 17 tests

[sovdeeth]

2 parallel tasks, 2.14 tests (1.21+)