Use package metadata for version and remove version.py

[shanejbrown]

This PR does two things:

1. Revert to d909509

• Reverts the version-fix and version-fix2 work so the codebase is back to the state at that commit.

2. Single source of truth for version

• buildrunner/init.py: Reads version with importlib.metadata.version("buildrunner"), falling back to "DEVELOPMENT" when the package is not installed (e.g. in development). Removes the old version.py loading and unused types import.
• buildrunner/config/loader.py: Drops VERSION_FILE_PATH and file-based version reading. Uses buildrunner.version for config version validation and treats "DEVELOPMENT" as “skip validation” with a warning.
• Tests: tests/test_version.py no longer uses a real version.py or VERSION_FILE_PATH; it patches buildrunner.version to cover valid version, DEVELOPMENT, single-component version, config-too-high, and non-numeric version.

Version is now defined only in pyproject.toml and consumed via standard package metadata, with no version.py file.

What does this PR do?

What issues does this PR fix or reference?

Previous Behavior

New Behavior

Merge requirements satisfied?

• I have updated the documentation or no documentation changes are required.
• I have added tests to cover my changes.
• I have updated the base version in pyproject.toml (if appropriate).