version source class improvements

[beckermr]

Some items we ran into recently:

• the naming of meta_yaml in the variable name of the methods (fix: clean up cruft in source version fetching and include excludes #4829)
• the naming of meta_yaml in the node attributes
• unclear expectations around error handling (fix: clean up cruft in source version fetching and include excludes #4829)
• testing code with unclear patterns
• type hints (fix: clean up cruft in source version fetching and include excludes #4829)
• doc strings (fix: clean up cruft in source version fetching and include excludes #4829)
• what to log vs not (fix: clean up cruft in source version fetching and include excludes #4829)
• account for excluded versions when fetching to simplify bot logic (fix: clean up cruft in source version fetching and include excludes #4829)

cc @jaimergp