Rework build system and test execution

This updates C tests to run only as one binary.

The important change is that tests are enabled explicitly and thus in
default disabled. The same now also applies to linters.
8 jobs for rework-tests in 3 minutes and 46 seconds (queued for 5 seconds)
latest
Status Job ID Name Coverage
  Build
passed #556321
build-alpine

00:00:44

passed #556319
build-debian-stable

00:00:42

passed #556320
build-debian-unstable

00:00:41

 
  Test
passed #556322
check

00:01:10

passed #556324
lint-c

00:00:25

passed #556325
lint-lua

00:00:23

passed #556323
valgrind-memcheck

00:03:01

 
  Coverage
passed #556326
coverage

00:01:18

75.6%