feat(models): add cyvest v6 findings and evidence schema

[PakitoSec]

Summary

• introduce the Cyvest 6.0.0 data model across Python, schema, and JS packages, including schema_version, findings in place of checks, and evidence support
• update serialization, keys/levels helpers, CLI/examples, visualization payloads, and generated TypeScript types to match the new investigation shape
• refresh documentation with v6 terminology, package/version updates, and a migration guide for upgrading from v5

Testing

• adds coverage for the v6 model changes in tests/test_v6_models.py
• updates existing Python and JS tests that cover schema, getters/finders, graph handling, compare flows, CLI behavior, and shared context semantics