Add justfile, remove coveralls, and fix AUTOLOAD in CI

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Why?

In an effort to modernize and simplify our local tooling, we're moving our dev commands from makefiles to justfiles. This is intended to be mostly a drop-in replacement, but some command names may change per standardization efforts.

Namely, I renamed fmt to format, added lint in place of phpstan, and swapped vendor to install.

One actual change is that dependencies won't auto-install before running tests like they did before. Users will have to just install before just test.

Also, I didn't add a ton of docstrings, since the recipes are mostly self explanatory. But, we could add some. The recipes are also grouped, so the help output looks like:

Available recipes:
    [useful]
    install            # install vendored dependencies; only used locally
    test *options
    format *options

    [CI]
    ci-test
    format-check
    lint *options

    [misc]
    phpstan-baseline
    phpdoc

Without groups, output of just is:

Available recipes:
    install            # install vendored dependencies; only used locally
    test *options
    ci-test
    format *options
    format-check
    lint *options
    phpstan-baseline
    phpdoc

Which isn't bad either. I could go either way on the groups. If nothing else, I think it makes the justfile itself harder to grok, so i'm fine to pull them too.

CI

Also, there was an issue where we weren't correctly setting the AUTOLOAD env var, so we were never running tests with autoload=1. The justfile flagged this issue and I changed the way the matrix was loaded to acommodate it.

What?

• added justfile
• added warning to top of makefile
• tweaked CI to use just instead of make
• fixed CI so AUTOLOAD was correctly set
• removed PHPstan from a matrix and just hardcoded the version we wanted.

See Also

• DEVSDK-2325

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Since we're not running phpstan across multiple PHP versions, I just hardcoded the value we're using

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this never worked as intended: env doesn't actually set the environment, it just sets a github variable called env

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because just recipes can take arguments, we can replace the env-looking value with the actual value we want and pass it in directly

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This will show a nicer name now that we're not using the full AUTOLOAD string

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Because the names of the CI jobs changed, there's a mismatch on the required tests. We'll have to bypass some branch protections in PHP during the cutover, but should be smooth sailing after that.