[TEST] Create unit tests for utils/scaffold-stark/common.ts file

Fixes #372

Types of change

• Enhancement

Test covers

• Conversion of BigInt values to strings.
• Handling of non-BigInt values (returning them as-is).
• Validation of correct Ethereum addresses (40 hexadecimal characters with '0x' prefix).
• Rejection of invalid addresses (wrong length, missing prefix, invalid characters).
• Conversion of non-zero BigInt values to hexadecimal strings.
• Handling of zero as a BigInt.
• Validation of correct JSON strings (objects, arrays, and simple values).
• Rejection of invalid JSON strings (malformed JSON, non-JSON strings, empty strings).
• Test
  
• Test coverage