feat: add elapsed time field to shreds

[gacallea]

make the ui display elapsed time for each shred. something like this:

• [ ] use lua sodlib (os.time()?)
• [ ] callback function to pass to NUI
• [ ] find a way to run it continuosly from shred addition

[gacallea]

requesting backup: https://github.com/MunifTanjim/nui.nvim/discussions/325

[gacallea]

https://github.com/MunifTanjim/nui.nvim#extendibility (see timer extension example)

[gacallea]

https://github.com/akinsho/clock.nvim

https://neovim.io/doc/user/luvref.html#luv-timer-handle

[gacallea]

something like this but to count elapsed time up https://github.com/cbrgm/countdown.nvim

[gacallea]

if someone wants to help with timers, I'd be grateful. I can't get it to work. Stopping attempts for now.