Fix task exit status handling, uniformize process exit method and tests

[jchambon-equativ]

In this commit I mainly updated the $status handling in Task.php because the same variable was used for 2 purposes.
I also added the thread exit with posix when enabled.
And because the pest --filter option still executes all the test which aren't wrapped in a callable I managed to refactor the test file to fix this.

[jchambon-equativ]

@freekmurze hi ! Could you take a moment to take a look at this pull request please ? Thanks !

[freekmurze]

Thanks!

[sadiqsalau]

This pull request is crashing my laravel scheduled tasks due to:

posix_kill(getmypid(), SIGKILL); 

I'm getting errors for queries until I discovered this:

SQLSTATE[HY093]: Invalid parameter number (Connection: mysql, SQL: select * from `farmers` where `id` = 77 limit 1)

I have opened a discussion - #76

[freekmurze]

@jchambon-equativ could you take a look at this?

[jchambon-equativ]

@freekmurze: @sadiqsalau closed the conversation because the problem was elsewhere.