Run Cartesian product of values in parallel

[sam-mosleh]

Currently we can run a recipe sequentially like below:

OS := "linux windows"
ARCH := "x86_64 arm64"

run-all:
    @for os in {{OS}}; do \
        for arch in {{ARCH}}; do \
            just run-build $os $arch; \
        done; \
    done

run-build os arch:
    @echo "Running for: {{os}} - {{arch}}"

I'd ideally want to run it in parallel like this:

OS := "linux windows"
ARCH := "x86_64 arm64"

[parallel]
run-all: (run-build *OS *ARCH)

run-build os arch:
    @echo "Running for: {{os}} - {{arch}}"

Considering that [parallel] is implemented, the only missing part for this is to run a recipe multiple times based on the Cartesian product of values provided.

[casey]

I think this is covered by #558.