composer: use separate autoload and autoload-dev

[mfn]

Currently the whole project tree is marked for autoload, from composer.json

    "autoload": {
        "classmap": [
            "./"
        ]
    },

It does not differentiate between autoloading actual source and test related stuff, but should.

(unverified) suggestion:

    "autoload": {
        "classmap": [
            "./src/"
        ]
    },
    "autoload-dev": {
      "classmap": [
        "./tests/"
      ]
    }  

[jrfnl]

A PR is open to address in php-parallel-lint/PHP-Parallel-Lint#88

[grogy]

PR was merged. Thanks @mfn for suggestion and @jrfnl for pushing as PR 👍

[mfn]

Nice, closing then!