Fix trailing 0s on bitfield serialization

[austinabell]

Summary of changes
Changes introduced in this pull request:

• Trailing 0 was being added to end of serialized bytes in an edge case
  • Also added a loop to remove any other 0 bytes because @timvermeulen suggested that it may be possible for this to happen

538/592

Reference issue to close (if applicable)

Closes

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