Fix copy_on_select GTK toast spam

[jnichols0]

Fixes core issue for #4800, moves copy_on_select clipboard logic in src/Surface.zig out of setSelection and into handleMouseButton. When left mouse is released and the current selection is not empty, saves selection to clipboard and sends an adw toast. The selection will still be updated as the user drags, however the clipboard will be written to just once when the mouse button is released.

This patch doesn't add a delay to sending the toast as suggested, wasn't sure how to best do that without throwing it in an async function. Open to suggestions. :)

[jcollie]

I think adding a delay is unnecessary since the toast spam is fixed in a better way.

[jnichols0]

Latest commit fixes memory leak and removes log line.

[mitchellh]

The issue I have with this PR is that it makes it so that non-mouse selection (i.e. selection keybinds) do not update the selection clipboard. I'm not sure if that's intended behavior (I haven't checked other terminals that support it), but the way I currently expect selection to work is that any selection method would result in the selection keyboard being updated.

I think an alternate approach is needed here where maybe setSelection isn't changed, but our mouse events need to stop using it and set terminal.screen.select directly and then we call setSelection at the end (with the existing selection) in order to persist it once to the clipboard and avoid the toast spam.

[jnichols0]

Ah I see. I'll take another look.