[Phase 4] polkadot.js Compatibility Testing (Issue #44)

[gmajor-encrypt]

Summary

This PR adds a compatibility testing framework to ensure php-scale-codec produces the same encoding results as polkadot.js SCALE codec reference.

Files Added

compat/ directory:

• README.md - Documentation and usage
• package.json - Node.js dependencies for polkadot.js tests
• tests/test-vectors.json - Known good encoding values from polkadot.js
• tests/php-compatibility-test.php - PHP test runner
• tests/run-compatibility-tests.js - Node.js test runner
• tests/generate-test-data.js - Test data generator

Makefile:

• Added make compat target for running compatibility tests

Test Coverage

Category	Types	Status
Integers	U8, U16, U32, U64, U128, I8, I16, I32, I64	✅
Compact	Compact integers	✅
Boolean	bool	✅
String	Text, String	✅
Collections	Vec	✅
Option	Option	✅

Test Vectors

Test vectors in test-vectors.json contain:

• Input values (including edge cases: min, max, 0)
• Expected hex-encoded outputs from polkadot.js reference

Running Tests

# Run PHP compatibility tests
make compat

# Or directly
php compat/tests/php-compatibility-test.php

Tasks from Issue #44

• Prepare test dataset
• Write comparison test script
• Compare encoding/decoding results for all types
• Fix compatibility issues (to be identified after CI runs)
• Establish continuous comparison testing

---

Closes #44