[FR] Free RAM

### Description

As the notes are opened, they accumulate in the RAM memory. It would be really nice if the app freed up the RAM when a note was closed.

### Impact

There would be no risk of using too much RAM even with a lot of notes and images.

### Additional Context

Using AppImage in Linux Mint 21.1 XFCE.

To add more information I did a simple test. I openned a new folder and inserted a new note just with a calendar:

Them, I started to change between the two notes. The ram has started to go up indicating that for every time a note is opened, it is loaded into the ram memory, even if it has already been opened previously:
After about 1 minute of doing this, I got to +100MB of RAM accumulated as the screenshot shows. I waited about 20min to see if the RAM would decrease, but the consumption remains the same. This may seem like an exaggerated test at first, but I believe it is not. A user with a lot of notes that contain calendars, images, tables, etc. will probably reach a very high RAM consumption after some short time of use if they are constantly browsing between their notes.

I think I can't say this is a bug, so that's why I openned like a Feature Request.