Feature request: Hide/Collapse entire blocks

[RednibCoding]

Have you searched existing Github issues to see if someone has already requested this feature?
Yes

Describe the solution you'd like
Beeing able to hide/show blocks. Hidden blocks should be persistent accross restarts of heynote.

Describe alternatives you've considered
Currently i use a Plain Text block when i have notes in plain text that i want to be collapsable since Plain Text blocks always have a fold icon at the first line. Problem is that the state of folding is not persistent accross restarts of heynote. So when i restart heynote, i have to fold all notes again.

The solution could be to always show a fold icon at the start of a block, no matter what type of block. This fold state gets written to the buffer like so:

∞∞∞markdown*

Where the asterisk (or any other symbol indicates that the block is collapsed)

For this feature, i think feature #54 is important, or at least part of it. The part that the first line should be shown instead of the last line when a block is collapsed.

[hanoii]

Beeing able to hide/show blocks. Hidden blocks should be persistent accross restarts of heynote.

Yes, I also think this would be a great addition.