Make CI faster

[iffy]

I'm coming here from what @guzba mentioned here about slow macOS tests: https://github.com/treeform/pixie/pull/510

This PR makes CI faster for macOS. Here's a comparison:

	Currently	This PR
Total time	15-16min	8-9min
Cumulative CPU time	1h 14m 50s	21m 54s
Usage report	Latest	PR

Granted, there seems to be a flakey test that fails sometimes on macOS, so maybe some of the speedup comes from skipped tests? But if you compare a single macOS test run, you can see the savings during the install step latest 14:39 run vs this PR 0:48 run

I'm not offended if you don't want the PR -- close it if you don't. I just hate to see slow CI builds :)

[treeform]

This could be pretty cool if it works!

1.2.2 does not supply a binary?

[iffy]

1.2.2 does not supply a binary?

Unfortunately, binaries that work with macOS weren't produced until v1.2.6 AFAICT. If you do find a nightly URL that works for 1.2.2, you can specify it as described here: https://github.com/iffy/install-nim/blob/master/install-nim.sh#L24

As-is, this PR uses choosenim to install 1.2.2.

[amkrajewski]

Have you tried installing using Homebrew? I found it to behave as expected and during my testing workflow runs it installs nim (v2.0.0) in just about 5s on macos-14 runners or 11s on macos-12 runners.

In my specific case, is also appreciably faster than other runners. Installing (1) nim, (2) Arraymancer and wimpy (through nimble), (3) compiling my code, and (4) running all tests takes under 60s.

To be a bit more quantitative:

Runner	Install Tool	Install Time	Test Runtime
macos-14	Homebrew	5s	16s
ubuntu-latest	jiro4989	7s	30s
macos-12	Homebrew	11s	40s
windows-latest	Conda+jiro4989	185s	51s

There is no magic involved. Here is the job from my workflow YAML file:

test-M1:
    runs-on: macos-14
    steps:
      - name: Checkout
        uses: actions/checkout@v3
      - name: Install Nim with Homebrew
        run: brew install nim
      - name: Install dependencies
        run: nimble install -y arraymancer nimpy
      - name: Compile nimplex
        run: nim c -d:release nimplex.nim
      - name: Run grid tests
        run: nim c -r -d:release tests/runAll.nim

I hope it helps :)