Add new --matrix option to multiply commands

[cdrini]

Closes #517

Sample runs:

Single dimension:

$ dist/bin/concurrently.js --group --matrix 'A B C' 'echo {1}'
[0] A
[0] echo A exited with code 0
[1] B
[1] echo B exited with code 0
[2] C
[2] echo C exited with code 0

Multiple dimensions:

$ dist/bin/concurrently.js --group --matrix 'A B' --matrix '1 2' 'echo {1}{2}'
[0] A1
[0] echo A1 exited with code 0
[1] A2
[1] echo A2 exited with code 0
[2] B1
[2] echo B1 exited with code 0
[3] B2
[3] echo B2 exited with code 0

With environment variables:

$ SERVERS="$(echo ol-web{0..2})"
$ IMAGES="python:3.12-slim python:3.13-slim"
$ dist/bin/concurrently.js --group --matrix "$SERVERS" --matrix "$IMAGES" 'ssh {1} docker image pull {2}'
[0] 3.12-slim: Pulling from library/python
[0] af302e5c37e9: Pulling fs layer
[0] 499051ac08b3: Pulling fs layer
...
[0] bc54bb88b02b: Pull complete
[0] Digest: sha256:123be5684f39d8476e64f47a5fddf38f5e9d839baff5c023c815ae5bdfae0df7
[0] Status: Downloaded newer image for python:3.12-slim
[0] docker.io/library/python:3.12-slim
[0] ssh ol-web0 docker image pull python\:3.12-slim exited with code 0
[1] 3.13-slim: Pulling from library/python
[1] af302e5c37e9: Pulling fs layer
[1] 31fc40b7245b: Pulling fs layer
...
[1] e81d26d6c5a7: Pull complete
[1] Digest: sha256:23a81be7b258c8f516f7a60e80943cace4350deb8204cf107c7993e343610d47
[1] Status: Downloaded newer image for python:3.13-slim
[1] docker.io/library/python:3.13-slim
[1] ssh ol-web0 docker image pull python\:3.13-slim exited with code 0
[2] 3.12-slim: Pulling from library/python
[2] af302e5c37e9: Pulling fs layer
...

[coveralls]

coverage: 98.032% (-0.1%) from 98.18%
when pulling ecdae50 on cdrini:517/feature/matrix-option
into 7f3efb2 on open-cli-tools:main.

[gustavohenke]

Thanks for taking this up!
I made several suggestions and asked a few questions in this pass.

I'll update the docs to mention matrices as well in a follow-up, unless you feel like doing it while keeping it on brand?

[gustavohenke]

I assume the _ is to signal that the field is private - if there isn't another field with the same name (such as a getter), let's not add that prefix.
It can also be made readonly:

Suggested change

	private _bindings: string[][];
	private readonly bindings: string[][];

[gustavohenke]

This line isn't necessary, as the private in the constructor param list does the same job.

Suggested change

this.matrices = matrices;

[gustavohenke]

Doesn't seem like it's read outside of the constructor, so for now let's not make it a field

Suggested change

	constructor(private readonly matrices: readonly string[][]) {
	constructor(matrices: readonly string[][]) {

[gustavohenke]

Should an error be thrown if the placeholder isn't a number?
Might convert a "wtf is concurrently doing" to a "oh, my bad, I got it wrong" 😄

[gustavohenke]

Can you please update this comment? It looks like it's assuming some context from elsewhere.

[gustavohenke]

Looks like matrices have preference over passthrough arguments using the same {number} syntax. Was it intended?

It needs to be called out in the help and in the docs.