Improve dynamic versioning documentation (clarify regarding regex vs. python evaluation))

[nyoma-diamond]

Currently, dynamic versioning is performed by reading the provided file as a raw text file, even if it is a python file (e.g., __about__.py). This means hatch cannot parse the version if it parsed from elsewhere at build-time.

For example, suppose I have a separate YAML file with additional metadata about the project, I may want to parse the version (among other metadata) from that file at build-time. (I recognize this is a very strange case that can be worked around in different ways, but this is nonetheless a functional example to show how the documentation introduces confusion)

This causes confusion in the current versioning documentation (https://hatch.pypa.io/1.13/version/), which suggests referencing python files (e.g., __about__.py or __init__.py) to pull the dynamic version. This makes it somewhat unclear that these files are parsed literally as strings, and not evaluated at build-time. I'd suggest either changing these examples to not be python files, include non-python examples for comparison/clarification, and/or state more explicitly that the file at version.path is parsed as raw text.