Reader::seek doesn't rewind bits read, causing leftover slice error

[i404788]

Hey there I'm currently running into an issue with the Reader::seek implementation.

I've identified my specific case here:

deku/src/reader.rs

Lines 66 to 69 in 0902ae0

	SeekFrom::Current(n) => {
	if n > 0 {
	self.bits_read += (n * 8) as usize;
	}

I've made a custom reader till then end and then rewind some amount, as that is currently the easiest way to decode a certain packet:

// WARN: this is not efficient for high `bytes_left` values
fn read_until_remaining<R: Read + Seek>(
    reader: &mut Reader<R>,
    bytes_left: usize,
) -> Result<alloc::vec::Vec<u8>, DekuError> {
    let mut data = <alloc::vec::Vec<u8> as DekuReader<Limit<_, _>>>::from_reader_with_ctx(
        reader,
        Limit::end(),
    )?;
    data.truncate(data.len() - bytes_left);

    reader
        .seek(deku::no_std_io::SeekFrom::Current(-(bytes_left as i64)))
        .map_err(|e| DekuError::Io(e.kind()))?;

    Ok(data)
}

with a struct such as

    #[deku(reader = "read_until_remaining(deku::reader, 4)")]
    pub data: alloc::vec::Vec<u8>,

    pub status: u32,

This works (using logging to verify), however at the end it will slice out of bounds when trying to return the remaining/leftover data.
This is because we are re-reading previous bytes, which are already added to the bits_read cursor, but the internal reader will put it's cursor back.