Description

Adding a cache for SourceMetadata, similar to BuildMetadata.

If BuildMetadata is responsible for answering - what packages ( outputs ) from this package can build,
SourceMetadata is responsible for returning all outputs with run_exports and dependencies solved.

This PR aims to cache these results.

How Has This Been Tested?

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Claude

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation