these are properties that we don't really want to be immutable

this will be what enforces immutability at runtime

This is where the magic happens. Allowing for different levels of state
changes while ensuring any specific state reference is immutable.

Not yet tested for bugs.

This makes it much easier to make incremental changes to the current
state.

Also added a print function to maker debugging state values easier.

The copies are not readonly.

Only the most basic operations have been ported, there is still a LOT
of broken functionality.

Since the readonly tables contain a reference to the original table we
can't make the keys weak, at least not in Lua5.1. In Lua 5.2 weakly
keyed tables act as ephemeron tables, so they would probably work
there. I don't have a Lua5.2 build of mpv, so I can't test, but it might
be worth using ephemeral tables when Lua5.2 is detected.

String manipulation is quite costly in Lua, this significantly reduces
the number of garbage string produced and should help to speed up
scrolling and reduce garbage collection.

Reducing garbage collection is quite important since it directly impacts
the performance of read-only tables lookups by clearing the cache.

This prevents the sub-tables from being garbage collected from the cache
until the base read-only table has been garbage collected.

This should significantly reduce the number of new read-only tables that
are created while scrolling.