Fix multiple NumCollectorStateBugs

[pianistrevor]

• Use dtostrf() for printing entry with appropriate precision, rather than the original method of formatting a format string
• Fix bug where clearing value did not reset the factor of precision
• Add test coverage for clear to catch this

This fixes #273.

[pianistrevor]

The extra commits were the result of incorrect upstream merges; these will be squashed here and I've corrected the problem in main on my fork.

[jgfoster]

I've asked @prestoncarman to approve as well.

[prestoncarman]

LGTM