e9f63fdf86
Implement `Write for Cursor<[u8; N]>`, plus `A: Allocator` cursor support This implements `Write for Cursor<[u8; N]>`, and also adds support for generic `A: Allocator` in `Box` and `Vec` cursors. This was inspired by a user questioning why they couldn't write a `Cursor<[u8; N]>`: https://users.rust-lang.org/t/why-vec-and-not-u8-makes-cursor-have-write/68210 Related history: - #27197 switched `AsRef<[u8]>` for reading and seeking - #67415 tried to use `AsMut<[u8]>` for writing, but did not specialize `Vec`.