Add decimals-consistency guard rejecting register_offering with mismatched token decimals

[thlpkee20-wq]

Description

When payment_token_decimals is provided at registration it must match the on-chain payment-token contract's decimals(). Reject mismatches with a structured error to prevent display corruption.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: src/lib.rs, docs/multi-offering-payment-token-independence.md
• Guard must be robust to token contracts that revert on decimals()

Suggested execution

• Fork the repo and create a branch
• git checkout -b feat/decimals-consistency
• Implement changes
  • Query token decimals via cross-contract call
  • Compare with declared value
  • Reject with DecimalsMismatch
• Validate security and correctness assumptions

Test and commit

• Run tests
  • cargo test --all
• Cover edge cases
  • Token contract returning zero decimals and reverting decimals
• Include test output and security notes

Example commit message

feat: guard against decimals mismatch on register

Guidelines

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

[Gentleslyl2006]

Hello maintainer
I would like to work on this issue and I can fix it
Can I get it assigned?

[Gentleslyl2006]

Hi maintainer
I can fix this issue.
I'll make sure the implementation is tested, clean, and aligned with what's outlined here before submitting for review. I'm available to start right away and can share progress updates along the way.
Can I get this assigned to me?