Adding ontology converters

[vmihalovski]

OSI Ontology Converters — Python Project Setup

This PR introduces the converters/ontology package as a standalone, installable Python project providing bidirectional conversion between ontology formats used across the OSI ecosystem.

What's included

Three converters:

• Palantir → OSI — parses a Palantir ontology export (ZIP containing ontology and dataset spec JSON files) and converts it into an OSI ontology model, mapping Palantir object types, relations, and datasets to their OSI equivalents
• OSI → Spec — serialises an OSI ontology model into an OSI-compliant YAML specification
• Spec → OSI — parses an OSI YAML specification back into an OSI ontology model, enabling round-trip conversion

Project setup:

• pyproject.toml with runtime dependencies (pydantic, pyyaml) and dev extras (pytest, pip-tools)
• requirements.lock for fully reproducible installs via pip-tools
• src/osi/ package layout — the package is importable as osi after installation
• .gitignore covering Python artifacts, virtual environments, pyenv, VS Code, and JetBrains IDE files
• README.md with step-by-step setup instructions using pyenv and virtualenv

Script:

• scripts/palantir_to_osi.py — a ready-to-run CLI script that takes a Palantir export ZIP and outputs an OSI YAML to stdout, with optional Snowflake database and schema configuration via environment variables