fix ffi for platform-specific uint_fast types for macOS and Android

[KyrylR]

Fixes:

• macOS (x86_64 and arm64): uint_fast16_t is u16, not usize
• Android (Bionic libc): uint_fast16_t is u32, not u16
• jet FFI calls failing on Intel Mac and Android

Because of the previous setup I have encountered failures the one below:
Blockstream/gdk#221

[KyrylR]

I verified this fix on the Intel Mac only; for Android, it will require some time

[KyrylR]

Also, I am not sure about the

#[cfg(not(target_arch = "wasm32"))]
pub type c_uint_fast64_t = usize;

Because of: https://en.cppreference.com/w/c/types/integer.html

As far as I understand on 32-bit platforms like armv7 because we are using the usize this thing could fail

[apoelstra]

I verified this fix on the Intel Mac only; for Android, it will require some time

I'll take it anyway. This is definitely an improvement, in that it at least separates out the arches a bit to make it easy to edit individual ones.

[apoelstra]

If this approach doesn't work, another thing we can do is just patch the C code to #define these types as fixed-size ones which have Rust equivalents. We don't need the speed benefit that the Elements integration needs.

[KyrylR]

Verified via Docker for the Android build

[apoelstra]

ACK 7a77539; successfully ran local tests

[apoelstra]

Tagged and published.

[KyrylR]

Should I bump simplicity-lang version now?

UPD: bumped, let me know if there is a need to revert or update something

[KyrylR]

Merged in: 7f42b53