sqlcipher decryption

[belamu]

As a result of #133 this PR should retreive the necessary password for the encrypted key in gnome and kde and print suitable help messages in case it does not work.

As a side effect, also macOS users get a (hopefully helpful) error message in case of password retreival error.

The commits can also be used on their own, see their commit messages for their content.

[belamu]

Unfortunately I could not test the changes because I am on nixOS and there

• rye has problems working on nixOS which I could not figure out so far
• I could not get the signal-export nix package working (see bump signal export to 3.2.2 NixOS/nixpkgs#353086)
• when I just call python sigexport/main or python -m sigexport package metadata are missing or import of sigexport module is not working. (Even though I've worked a lot with python, packaging and modules and so on are very unclear to me.)

Update: uv (the successor of rye) is working on nixOS. But a) I am not familiar on how to use it and b) uv run sigexport gives ModuleNotFoundError: No module named 'html.entities'; 'html' is not a package somewhere in beautifulSoup4.

[carderne]

Nice thanks for putting this together! Merging

[carderne]

Available in 3.2.1 if you want to try it out

[belamu]

Tried it out and it's murks. Several typos made it worse for gnome and kde. Hopefully should still work with given password and macos.
Thanks to the help I got from @phaer at nix packaging I was able to try it out and will do a fixing pr when I have time in the next days.