feat: support passing data to script via YAML

[tobiasraabe]

Summary

This PR adds the first slice of the planned YAML configuration feature: a stronger stata_mock implementation that can emulate the relevant parts of the Stata yaml package.

The mock now supports:

• Stata /// line continuations
• yaml read using ..., locals replace
• custom local prefixes via prefix(...)
• expansion of returned macros such as `r(yaml_produces)'
• scalar-style yaml get database:host
• metadata-style yaml get indicators:CODE, attributes(...)
• basic yaml validate, required(...) types(...)
• rejection of unsupported YAML syntax such as anchors and aliases

This intentionally does not add the pytask-facing serializer feature yet. The goal is to get CI signal on the mock foundation first.

Checks

• uv run ruff check packages\stata_mock\src\stata_mock\cli.py tests\test_stata_mock.py
• uv run pytest tests/test_stata_mock.py
• uv run python -m compileall -q packages\stata_mock tests\test_stata_mock.py