The compact LSB-aligned encoding via ActiveBytes packed paths into
ceil(len/8) bytes without recording the bit-length. Two distinct paths
whose bit-lengths fell in the same byte-bucket and whose integer values
matched produced identical bytes — e.g. the 1-bit path "1" and the 8-bit
path "00000001" both encoded to [0x01], so two stems sitting at depths 1
and 8 on different branches could clobber each other in nodeset.AddNode.
Replace ActiveBytes/PutActiveBytes with KeyBytes/PutKeyBytes, which
append a uint8 bit-length byte after the active bytes. Postpend (rather
than prepend) so nodes along a single root-to-leaf descent share leading
path bytes, improving LSM block locality during traversal.
The empty path is encoded as no bytes (not [0x00]): byteCount=0 is
unique to len=0 so no disambiguation byte is needed. This keeps the
root's DB key empty, matching the resolver's existing nil-path convention.
