Fix new and deleted methods and add variadic functionality

[martinvuyk]

Hi, pretty amazing project. I was thinking of starting a FlatBuffer impl when I came across this.

There is still a lot of code that won't be functional, I saw a Tuple inside a list in a Cache struct somewhere, rn Tuple doesn't conform to CollectionElement sadly.

I added some variadic input into your add funcs, and an idea of taking in a FlexVec as input for the map with a key. Other than that the changes are mostly to fix broken changes since the latest mojo release

Cheers!