feat: Add KYC verification for plan creation and claiming

[zintarh]

Overview

This PR implements KYC verification for inheritance plan creation and claiming, ensuring only approved users can interact with these critical functions.

Changes

Core Implementation

• ✅ Added KycStatus enum with Pending, Approved, and Rejected states
• ✅ Added KycStatus(Address) to DataKey for persistent storage
• ✅ Implemented set_kyc_status() and get_kyc_status() functions
• ✅ Added KycNotApproved error type to InheritanceError enum

Plan Creation Protection

• ✅ Added KYC pre-check in create_inheritance_plan() function
• ✅ Returns KycNotApproved error if user's KYC status is not approved
• ✅ Blocks pending and rejected users from creating plans

Plan Claiming Protection

• ✅ Implemented new claim_plan() function with KYC verification
• ✅ Verifies claimant's KYC status before allowing claim
• ✅ Validates email and claim code against plan beneficiaries
• ✅ Returns appropriate errors for unauthorized attempts

Testing

• ✅ Comprehensive unit tests for KYC status management
• ✅ Tests for approved users successfully creating and claiming plans
• ✅ Tests for pending/rejected users being blocked
• ✅ Tests for proper error messages
• ✅ Tests for invalid claim credentials

Requirements Met

✅ Pre-check before creating a plan: Verifies user's KYC status is approved
✅ Pre-check before claiming a plan: Verifies user's KYC status is approved
✅ Descriptive errors: Returns KycNotApproved error for unauthorized attempts
✅ Comprehensive tests: All scenarios covered with unit and integration tests

Testing

All tests pass successfully:

• Approved users can create and claim plans ✅
• Pending users are blocked from creating/claiming ✅
• Rejected users are blocked from creating/claiming ✅
• Proper error messages are returned ✅

Closes #71