fix(build): Fix module changes not getting picked up

Previously, we left out the dependency of the QSTR header on modules.h. This was done to prevent rebuilds of the entire MicroPython sources whenever a Pycardium module is changed. This leads to issues where QSTRs got out of sync and weird errors like the following could happen:

import foo_module

Exception: No module `abc_def` (a different string than expected)

Attempt to fix this by only updating the QSTR header when the module-header actually changes. For this, a few workarounds are needed:

• Replace symlinks with actual copied files so timestamps change on updates.
• Add a hack so meson picks up on the dependency of the file in genhdr/

Co-authored-by: dx dequis@dequis.org

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@schneider: Please test whether this works on your system as well ;)