* FIX: Recursively tag topics with missing ancestor tags
Given only a child tag, walk up the ancestry chain, get all of it's
ancestors for use in tagging a topic
* FIX: Ensure only one parent tag is returned for topic tagging
Current implementation selects and return first parent tag if child tag
has multiple parents.
This change updates recursive parent tag implementation to only return
parent tags via only one ancestry line.
* DEV: Add test case for tag cycles
Given we aren't performing a strict graph traversal to get a tag's
parent, cycles do not have any effect on the tags returned for topic
tagging.
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