Fix sync messages logic

[austinabell]

Summary of changes
Changes introduced in this pull request:

• Cleaned up FillTipset to remove need to clone, error response is the input tipset if it fails to load
• Fixed logic in tipset bundle construction logic.
  • There was a lot of janky logic and weird indexing, so I just rewrote it (also avoids clones this way)

Reference issue to close (if applicable)

Closes

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