Rewrite code generation and upgrade to Pydantic v2

[pederhan]

Rewrites the code generation functionality and migrates all models to use Pydantic V2.

Code Generation

All code generation files are now located in the codegen directory.
The following new Hatch scripts have been added:

• generate-main: Generate main API models
• generate-scanner: Generate scanner API models
• generate: Generate all models (runs generate-main and generate-scanner)

The existing Justfile has been deleted as a result of migrating these scripts to Hatch.

Pydantic V2

Models have been changed to use Pydantic V2, which includes changes to validators and aliases. Changes are documented in the changelog.

Other

• Pre-commit now formats source files with Ruff instead of Black.