chore(saves): clean up cache that backs list of saves

[marcin-kozinski]

Clean up unused functionality and other tech debt around our last remaining usage of SyncCache/DataSourceCache.

• It wasn't using diffs produced by the built in usage of DiffUtil.
  • Removed the configuration option that was effectively always false and removed the effectively unused code and callback parameter.
• It wasn't using merges or dependencies.
  • This simplified loading, checking loading status and error handling a bunch.
  • "Ignore white-space changes" might be helpful in reviewing this.
• There were a few more unused methods.
• Moved updating StateFlow value to the official update extension function, from our bespoke edit wrapper.
• Tweaked implementation of NoCompareMutableStateFlow to avoid inheritance explicitly discouraged in (Mutable)StateFlow docs.

References

PR Checklist

Setup:

• Described changes for automated release notes in PR title using
  Conventional Commits standard
• Self Review (review, clean up, documentation)
• Basic Self QA

Review:

• Code Review approved

[nzeltzer]

lgtm