Currently we enforce that our code only runs on machines with a
certain pointer width (32 or 64 by failing to compile if pointer size
width is 16). One of the underlying reasons is because of requirements
in consensus code in Bitcoin Core which requires containers with more
than 2^16 (65536) items [0].
We can better express our requirements by asserting on Rust's index
size (the `usize` type).
As a side benefit, there is active work [1] to make Rust support
architectures where pointer width != idex size. With this patch applied
`rust-bitcoin` will function correctly even if that work progresses.
- [0] https://github.com/rust-bitcoin/rust-bitcoin/pull/2929#discussion_r1659399813
- [1] https://github.com/rust-lang/rust/issues/65473
c427d8b213