src: use `uintptr_t` to ensure a positive address

On Ubuntu 32-bit I was seeing values that were negative.
This fixes that.
src: use `NanEscapableScope` where appropriate

Any function that's not `NanReturnUndefined()`.
ref: add `hexAddress()` function

Safe to use for displaying memory addresses.
`address()` is not.
ref: use `hexAddress()` for the Buffer inspect() override

Safer to use this function than `address()` since it could overflow.