upstream backend changes from jocalsend

[nebkor]

This PR adds:

• updated Tokio and Tower deps
• HTTPS
• persistent configuration
• no more UI implementation mandated (no more native_notifications; events are sent over MPSC channels that any front-end UI can react to as they wish)
• support for sending text without an actual file existing

See https://git.kittencollective.com/nebkor/joecalsend for a full TUI application using it.

I know this is a massive change, so feel free to turn it down :) I needed to make most of these changes to support my TUI client already, so my needs are met (I've effectively forked your original code; this is the cleaned-up version of that, stripped of the frontend stuff I added).

I will also note that I did not use any AI for this.

[nebkor]

ditching UUIDs for Julids means that things like sessions are sortable

[wylited]

Hi, thank you for taking the time to make a PR. This looks great, I appreciate the support for my very badly put together library.

[nebkor]

Hi, thank you for taking the time to make a PR. This looks great, I appreciate the support for my very badly put together library.

my pleasure, thanks for putting something together in the first place!

I made a couple other changes in my fork that aren't here, that made a big difference:

• when starting the service, set the multicast TTL to 1 and disable loopback; previously, it would get confused about its own IP when it received a multicast datagram from itself that originated with a peer
• when initiating an outbound transfer request (so, need to wait for the peer to approve), don't block the main thread and instead spawn a Tokio task to wait for approval etc.