toOwnedSlice

    pub fn toOwnedSlice(a: *Allocating) Allocator.Error![]u8 {
        const old_memory = a.writer.buffer;
        const alignment = a.alignment;
        const buffered_len = a.writer.end;

        if (old_memory.len > 0) {
            if (buffered_len == 0) {
                a.allocator.rawFree(old_memory, alignment, @returnAddress());
                a.writer.buffer = &.{};
                a.writer.end = 0;
                return old_memory[0..0];
            } else if (a.allocator.rawRemap(old_memory, alignment, buffered_len, @returnAddress())) |new| {
                a.writer.buffer = &.{};
                a.writer.end = 0;
                return new[0..buffered_len];
            }
        }

        if (buffered_len == 0)
            return a.writer.buffer[0..0];

        const new_memory = (a.allocator.rawAlloc(buffered_len, alignment, @returnAddress()) orelse
            return error.OutOfMemory)[0..buffered_len];
        @memcpy(new_memory, old_memory[0..buffered_len]);
        if (old_memory.len != 0) a.allocator.rawFree(old_memory, alignment, @returnAddress());
        a.writer.buffer = &.{};
        a.writer.end = 0;
        return new_memory;
    }