This will make it slightly easier to port mm_port_serial_at_command() to
use GTask, since we won't have to keep a pointer to the result in GTask
after _finish() has been called.

In most cases the caller needs the value anyway, so this doesn't add too
much hasle.

GCC 13 is unhappy to cast a MMLogLevel to a guint32:

  [188/539] Compiling C object src/plugins/test-shared-icera.p/icera_tests_test-modem-helpers-icera.c.o
  In file included from ../src/plugins/icera/tests/test-modem-helpers-icera.c:27:
  ../src/mm-log-test.h:25:1: warning: conflicting types for ‘_mm_log’ due to enum/integer mismatch; have ‘void(void *, const gchar *, const gchar *, const gchar *, guint32,  const gchar *, ...)’ {aka ‘void(void *, const char *, const char *, const char *, unsigned int,  const char *, ...)’} [-Wenum-int-mismatch]
     25 | _mm_log (gpointer     obj,
        | ^~~~~~~
  In file included from ../src/mm-log-test.h:20:
  ../src/mm-log.h:61:6: note: previous declaration of ‘_mm_log’ with type ‘void(void *, const gchar *, const gchar *, const gchar *, MMLogLevel,  const gchar *, ...)’ {aka ‘void(void *, const char *, const char *, const char *, MMLogLevel,  const char *, ...)’}
     61 | void _mm_log (gpointer     obj,
        |      ^~~~~~~

That's perfectly fine, just use the enum type directly.

GCC 13 is unhappy about mixing enums and ints. However, if we fix the
type un mmtty's _mm_log() prototype, the compiler will find something
else to be irritiated about:

  [1/2] Compiling C object test/mmtty.p/mmtty.c.o
  ../test/mmtty.c: In function ‘_mm_log’:
  ../test/mmtty.c:283:5: warning: enumeration value ‘MM_LOG_LEVEL_MSG’ not handled in switch [-Wswitch-enum]
    283 |     switch (level) {
        |     ^~~~~~
  [2/2] Linking target test/mmtty

Fix that first.

Fixes https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/483

Different options are set as `feature`, also every possible plugin,
but this may cause confusion.

All options set as `feature` but plugins have been made `boolean` to
avoid further confusions.

`help2man` is also installed in the CI image because is required to
build different libraries.

Use G_GUINT64_FORMAT to properly format a guint64 type.

  ../test/lsudev.c: In function ‘println’:
  ../test/lsudev.c:68:5: warning: function ‘println’ might be a candidate for ‘gnu_printf’ format attribute [-Wsuggest-attribute=format]
     68 |     g_string_append_vprintf (output, fmt, args);
        |     ^~~~~~~~~~~~~~~~~~~~~~~