SAMADCON 0.6.7

Multi-line administrative template values no longer take the backend down.

A tester saved "Remove Default Microsoft Store packages from the system"
with a list of package names and got an HTTP 502 - and was signed out,
as was everyone else signed in to that console.

What happened. Since 0.6.6 SAMADCON packs Registry.pol itself, and it
handed Samba's preg binding a list for a multi-string (REG_MULTI_SZ). The
binding does not raise on that: it trips a C assertion (PyBytes_Check)
and aborts the process. nginx answered 502, and since sessions live in
the backend's memory, they went with it. Nothing was written - the abort
came before the file was saved - so affected policies are unchanged.

Only values of type REG_MULTI_SZ were affected: the template elements
shown as a multi-line text box. Check boxes, numbers, single-line text
and lists of values were not.

The fix. Measured in the image: preg takes and returns a multi-string
as one block of bytes - each string UTF-16LE with its terminator, then one
more. SAMADCON now builds that block when writing and splits it back into
its strings when reading, which it also got wrong.

Why it got through. The binding was only exercised by the integration
tests, which CI does not run. A new test now packs and reads back every
value type through Samba's own binding in the CI image. Pushed before the
fix, it aborted CI at the tester's package names; with the fix, it passes.

Checked on a Samba 4.22 DC: a policy with two multi-line fields saved,
edited and saved again - the lines in Registry.pol as entered, the
removed line gone, the version advanced once per save.

Images: ghcr.io/onlinecrash24/samadcon:0.6.7, :0.6 and :latest.