add: fuzz tests for unpacking functions

[nicoan]

Summary

This PR adds several property/fuzz testing for unpacking functions

Changes Made

• add unpacking test of heap uint string and uint
• add unpacking fuzz tests of heap uint, string and uint
• add unpacking fuzz tests for enums
• add unpacking ref fuzz tests
• add unpacking structs fuzz tests
• add unpacking enum fuzz tests

Checklist

• I have read the contributing guidelines.
• I have added/updated tests where appropriate.
• I have run relevant tests locally.
• I have updated relevant documentation (if applicable).
• I have disclosed any AI assistance per AI_POLICY.md.