Updated the spec (and the rust implementation):

• The order in which to serialize the entries s_i: v_i is not fully specified, but there are some constraints:
  • intuitively: Natural numbers less than 2^32 - 1 are sorted ascendingly
  • formally:
    • a key is called a more-or-less integer key if it is either the string "0", or a nonzero decimal digit (1 - 9 (0x31 - 0x39)) followed by zero or more arbitrary decimal digits (0 - 9 (0x30 - 0x39)) and consists solely of such digits
    • a key is called an int key if it:
      • is a more-or-less integer key
      • its numeric value is strictly less than 2^32 - 1
        • no, there's no off-by one error here: 0xfffffffe is an int key, whereas 0xffffffff is not
        • Why? We have no idea either
    • all entries with int keys must be serialized before all other entries
    • among themselves, the int keys are sorted:
      • by length first (ascending), using
      • numeric value as a tie breaker (the key whose raw bytes interpreted as a natural number are larger is serialized later)
        • note that this coincides with sorting the decimally encoded numbers by numeric value
  • all other entries may be serialized in an arbitrary order