Handle inference of multiple size for `Int` literals

[Champii]

We currently only support Int64 when inferring integer literals.
We need a way to have a "generic" int that is either bound by constraints when used in the program or defaulting to Int64 if no particular need is expressed.

This fails with a type error between the 10 number literal that is an Int64 and the bar field that requires an Int16

struct Foo
  bar: Int16

main: ->
  let foo = Foo bar: 10
  foo.bar

[Champii]

We might need a proper type inference system with sub-typing support