Datasource cleanup: introduce some types and avoid pass-by-context

[evankanderson]

Summary

While working on #5094, I discovered that there was some over-use of any and reflection that (IMO) made the code harder to understand. This hopefully contributes to polishing datasources for release.

Change Type

Mark the type of change your PR introduces:

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Tested with go test, which was helpful for finding all the places where signatures changed. Otherwise, this should be a no-op.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[teodor-yanev]

lgtm