fileMemoryMapSetLength

fn fileMemoryMapSetLength(
    userdata: ?*anyopaque,
    mm: *File.MemoryMap,
    new_len: usize,
) File.MemoryMap.SetLengthError!void {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    _ = ev;

    const page_size = std.heap.pageSize();
    const alignment: Alignment = .fromByteUnits(page_size);
    const old_memory = mm.memory;

    if (alignment.forward(new_len) == alignment.forward(old_memory.len)) {
        mm.memory.len = new_len;
        return;
    }
    return error.OperationUnsupported;
}