Defer source key import

[rmol]

Description

Stop importing source GPG keys during sync. We have a place on Source to store fingerprint and key, which is all we need for the import, and which is what we check when deciding whether to enable the reply box, so let's just update the database here and defer import to the keyring until someone actually wants to reply. It takes milliseconds that won't be noticed then, but do add up during sync.

This is based on and should be reviewed after #1034.

Test Plan

Run the SD core dev server. Run the client with run.sh and a fresh data directory. Ensure that you can still reply to sources. If you can, then deferring the key import until replying is working.

Checklist

If these changes modify code paths involving cryptography, the opening of files in VMs or network (via the RPC service) traffic, Qubes testing in the staging environment is required. For fine tuning of the graphical user interface, testing in any environment in Qubes is required. Please check as applicable:

• I have tested these changes in the appropriate Qubes environment
• I do not have an appropriate Qubes OS workstation set up (the reviewer will need to test these changes)
• These changes should not need testing in Qubes

If these changes add or remove files other than client code, packaging logic (e.g., the AppArmor profile) may need to be updated. Please check as applicable:

• I have submitted a separate PR to the packaging repo
• No update to the packaging logic (e.g., AppArmor profile) is required for these changes
• I don't know and would appreciate guidance

[eloquence]

(Per PR body, labeled blocked until #1034 is merged.)

[sssoleileraaa]

After removing the unused GpgHelper from update_sources and update_local_storage, I think this is good to go! This change makes a lot of sense. We no longer import the source key until we call encrypt_to_source. In the meantime I'll be checking out how much this improves performance. 🎉

[sssoleileraaa]

Once #1039 is fixed this can be merged.