Add currency-symbol and ISO-4217 code metadata field per offering for display

[thlpkee20-wq]

Description

Front-ends need a canonical currency symbol and ISO-4217 code per offering to render amounts correctly. Add optional metadata fields validated on register_offering.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: src/lib.rs, README.md
• ISO-4217 must be a 3-letter uppercase ASCII code

Suggested execution

• Fork the repo and create a branch
• git checkout -b feat/iso4217-metadata
• Implement changes
  • Add currency_iso4217 and currency_symbol fields
  • Validate format on register
  • Emit metadata in offering_registered event
• Validate security and correctness assumptions

Test and commit

• Run tests
  • cargo test --all
• Cover edge cases
  • Lowercase code rejection and 2- or 4-letter code rejection
• Include test output and security notes

Example commit message

feat: add currency ISO-4217 metadata per offering

Guidelines

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours

[Gentleslyl2006]

Hello maintainer
If this issue get assigned to me. You're guaranteed perfect results in return. I can fix it