feat: add property-based testing with QuickCheck

- Add quickcheck and quickcheck_macros dependencies
- Create comprehensive property tests for core components:
  - Pid: serialization roundtrip, node semantics, equality properties
  - Serialization: message roundtrip, envelope wrapping, wire format
  - EPMD: protocol serialization, node info properties
- Add PROPERTY_TESTING.md documentation
- All 37 property tests passing (11 pid + 11 serialization + 15 epmd)

Property tests verify invariants across hundreds of random test cases,
providing better coverage and edge case discovery than unit tests alone.

Author: am-kantox