Fix an Encoding Bug (200 Gold)

[mikera]

All CVM Values (and constituent Cells) have an Encoding, which is a unique representation of the Cell value in a byte sequence.

This bounty is for finding an Encoding bug and fixing it.

Requirements:

• A test case must be created that proved a failure in a fundamental Encoding rule, for example:
  • Two different Encodings that produce the same Cell value (as tested with ACell.equals)
  • Two different Cell values that produce the same Encoding
  • An Encoding which appears to produce a valid Cell (can be decoded successfully with Format.readXXX and passes ACell.validateXXX) but in fact the Cell has some flaw (i.e. a violated invariant that may break assumptions elsewhere in the code base)
• The root cause of the issue must be identified
• A PR must be contributed and accepted that adds the test case, and fixes the defect
• If appropriate, a PR must be contributed and accepted that updates the Encoding CAD (https://github.com/Convex-Dev/design/tree/main/cad/003_encoding)