Store calibration units in mm, UI input of either inches or mm

[thatcomputerguy0101]

Description

Extension of #2479 that also changes the backend to use millimeters instead of inches.

Meta

Merge checklist:

• Pull Request title is short, imperative summary of proposed changes
• The description documents the what and why, including events that led to this PR
• If this PR changes behavior or adds a feature, user documentation is updated
• If this PR touches photon-serde, all messages have been regenerated and hashes have not changed unexpectedly
• If this PR touches configuration, this is backwards compatible with all settings going back to the previous seasons's last release (seasons end after champs ends)
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