Feature/382 contract migration tools

[Oluwasuyi-Timilehin]

#closes #382

📋 Description

This pull request improves the TeachLink contract migration workflow by hardening upgrade initialization, adding migration metadata validation, and improving rollback test coverage.

Contract: contracts/teachlink/src/upgrade.rs now enforces valid state and migration hashes, auto-initializes upgrade state when absent, and includes stronger rollback expiry behavior. contracts/teachlink/src/lib.rs now initializes the upgrade subsystem during bridge contract initialization.

🎯 Type of Change

• ✅ Bug fix / stability improvement
• ✨ New feature
• ⚡ Performance improvement
• 🧪 Test coverage

📝 Changes Made

• Added upgrade::ContractUpgrader::initialize(&env)? to TeachLinkBridge::initialize(...) in contracts/teachlink/src/lib.rs.
• Updated contracts/teachlink/src/upgrade.rs:
  • prepare_upgrade and execute_upgrade now auto-initialize upgrade storage if UPGRADE_VERSION is missing.
  • prepare_upgrade rejects an empty state_hash.
  • execute_upgrade rejects an empty migration_hash.
• Added a dedicated regression test test_prepare_upgrade_auto_initializes.
• Extended test_rollback_window_expiry to move the ledger past the rollback window, confirm rollback is rejected, and verify rollback availability is cleared.

🔗 Related Issue(s)

• No issue number provided

🧪 Testing

Recommended commands

cd c:\Users\HomePC\Documents\D\teachLink_contract
cargo build --release --target wasm32-unknown-unknown -p teachlink-contract
cargo test -p teachlink-contract
cargo fmt --all -- --check
cargo clippy --all-targets --all-features

Notes

• cargo was unavailable in the editor terminal environment used for file edits, so please run the commands locally to verify the build and test pass.

🔍 Review Checklist

• Code follows repository style guidelines
• Added or improved tests for upgrade lifecycle behavior
• No new compiler diagnostics in modified files
• No secrets or sensitive data committed

💥 Breaking Changes

• This PR introduces breaking changes
• N/A: additive validation and initialization fixes only.

🚀 Deployment Notes

• Requires contract redeployment
• Requires data migration
• No deployment changes required beyond normal contract rebuild and redeploy

---

Ready for Review: yes

#closes

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[Xhristin3]

@Oluwasuyi-Timilehin resolve conflicts.