Add more ergonomic usage of Buffer protocol with SIMPLE flag.

[gatesn]

PyBUF_SIMPLE is a flag used to denote a buffer is a pure 1-dimensional contiguous unsigned u8 array.

This is a pretty common use-case, so we should make it close to trivial to map back and forth to Zig []u8.

In fact, we could support quite a lot of the 1-dimensional buffer protocol using comptime.

• []u8 -> writable simple
• []u32 -> writable, check format string, check alignment, etc.
• []const u32 -> readonly, etc.

[delta003]

Related -> #29