test: add ListingRegistry Hardhat suite

[TUPM96]

Summary

• add a minimal Hardhat setup for Nobay contracts
• add ListingRegistry tests for EIP-712 signature validity and tampering rejection
• cover ListingVerified/ListingRevoked events plus stored seller, URI, timestamp, active state, and listingCount accuracy
• ignore generated Hardhat and Node outputs

Validation

• npm test passes: 10 ListingRegistry tests
• npm run compile passes
• git diff --cached --check passed before commit

Closes #3

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