Feat/add test coverage

[phessophissy]

Summary

This PR adds a comprehensive test suite for the Renzo Protocol contracts, which currently lack test coverage in the public repository.

Changes

• Added 6 test files covering core contracts
• Added 4 mock contracts for isolated unit testing
• Added shared test utilities and fixtures
• Added test documentation

Test Coverage

Contract	Tests Added
RoleManager	25+ tests (roles, permissions, access control)
EzEthToken	30+ tests (mint, burn, transfer, allowances)
RenzoOracle	20+ tests (price lookups, calculations)
DepositQueue	18+ tests (fees, configuration)
STETHShim	6 tests (Chainlink interface)
BalancerRateProvider	12+ tests (rate calculations)

Running Tests

npm install
npm run compile
npm test