Fix Hatch code version source schema

[15r10nk]

Summary

• allow Hatch version sources that use both source and path, such as source = code
• model code version source options including expression and search-paths
• keep source-only version plugins separate from path-based configuration
• add a Hatch fixture for the documented code version source configuration

Validation

• node ./cli.js check --schema-name=hatch.json
• pnpm exec prettier --config .prettierrc.cjs --ignore-path .gitignore --check src/schemas/json/hatch.json src/test/hatch/version-code-source.toml
• uv run --with jsonschema python ... checked all src/test/hatch/*.toml as valid
• uv run --with jsonschema python ... checked all src/negative_test/hatch/*.toml remain invalid
• validated inline-snapshot's [tool.hatch] table against the patched schema

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @madskristensen and @hyperupcall - if they write a comment saying "LGTM" then it will be merged.

[hyperupcall]

Thanks