[OSSIE][NVIDIA_GSF] Add bidirectional GSF semantic model converter

[liofnv]

Summary

Adds an offline, bidirectional converter between Apache Ossie YAML and NVIDIA GSF semantic-model YAML.

• ossie-gsf export: Ossie → NVIDIA GSF
• ossie-gsf import: NVIDIA GSF → Ossie
• Python string-in/string-out API
• No GSF, Neo4j, database, or network connection required for conversion
• NVIDIA-specific metadata uses the NVIDIA_GSF custom-extension identifier

Why

GSF stores its active semantic layer in Neo4j. Its standalone semantic-model YAML provides a portable representation that can be versioned, reviewed, and converted without connecting directly to a GSF deployment.

Mapping

• Semantic model → GSF model
• Dataset → Term
• Physical field → ColumnAttribute
• Computed field or metric → SqlAttribute
• Relationship → semantic foreign key
• Expression dialects and vendor metadata are preserved for round trips

Testing

• 19 converter tests
• Checked-in Ossie/GSF fixture pair
• Bidirectional semantic round-trip coverage
• Generated Ossie YAML validated with the repository’s official schema and SQL validator
• Manually verified through the full CLI and live Neo4j import/export path

Notes

The physical catalog must already be ingested before the generated model is loaded into GSF.

The corresponding GSF import/export implementation is available on:
https://github.com/NVIDIA/GSF/tree/feature/ossie-import-export