Add comprehensive testing infrastructure for contracts

[chukwudiikeh]

Summary

This PR implements comprehensive testing infrastructure across 4 distinct testing dimensions for the Atomic Patent protocol:

• WASM Size Regression Check (Add contract WASM size regression check #891): Script and test suite to track compiled contract sizes and prevent unintended bloat
• Coverage Report & Threshold Gate (Add a coverage report and threshold gate for both contracts #892): Integration with cargo-llvm-cov for code coverage reporting with enforced floor thresholds
• Smoke Test Runtime Budget (Add a smoke test for the full re-enabled test suite runtime budget #893): Runtime enforcement to ensure test suite execution stays within performance budgets
• Differential Fuzzing Harness (Add a differential fuzzing harness between the two contracts' error-handling conventions #894): Fuzzing tests for error handling consistency between ip_registry and atomic_swap contracts

Test Coverage

All implementations include comprehensive test suites:

• ✅ wasmSizeCheck.test.js - 8 test cases for WASM size tracking
• ✅ coverageThreshold.test.js - 12 test cases for coverage gates
• ✅ smokeTestBudget.test.js - 11 test cases for runtime budgets
• ✅ contractErrorHandling.test.js - 14 test cases for error handling audit
• ✅ differentialFuzzing.test.js - 14 test cases for fuzzing and edge cases

Implementation Details

Scripts Added

• scripts/check-wasm-size.sh - WASM size regression detector
• scripts/coverage-threshold-gate.sh - Coverage floor enforcement
• scripts/smoke-test-budget.sh - Runtime budget checker
• scripts/coverage-config.json - Coverage configuration
• scripts/wasm-size-baseline.json - WASM size baseline tracker

Test Files

• src/__tests__/wasmSizeCheck.test.js
• src/__tests__/coverageThreshold.test.js
• src/__tests__/smokeTestBudget.test.js
• src/__tests__/contractErrorHandling.test.js
• src/__tests__/differentialFuzzing.test.js

Closes #891

Closes #892

Closes #893

Closes #894

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