func (c *writableChunk) writeAsFits(b []byte) int {
	if len(b) > c.contents.BytesRemaining() {
		b = b[:c.contents.BytesRemaining()]
	}

	c.checksum.Add(b)
	c.contents.WriteBytes(b)

	written := len(b)
	c.size += uint16(written)
	return written
}
func (c *writableChunk) writeAsFits(b []byte) int {
	if len(b) > c.contents.BytesRemaining() {
		b = b[:c.contents.BytesRemaining()]
	}

	c.checksum.Add(b)
	c.contents.WriteBytes(b)

	written := len(b)
	c.size += uint16(written)
	return written
}
// writeAsFits writes as many bytes from the given slice as fits into the chunk