Date Published appends AD (anno domini) to 4-digit years in Citations

Problem/Motivation

When using a CSL that shows the Date Published field, Bibcite appends AD to the 4-digit year, even though the CSL specification says that AD is only added to 2-digit years (and BC is appended to negative years). https://docs.citationstyles.org/en/stable/specification.html#ad-and-bc

Steps to reproduce

1. In a site with Bibcite entities enabled, create a reference with Date Published filled in. My example was a Journal Article.
2. Make sure you are displaying citations with a CSL that shows Date Published. I used Chicago Manual of Style 16th ed., which puts Date Published in parentheses before the Year of Publication.
3. Create a citation list. A view with the "Reference: Citation" field will work. Make sure the CSL from step 2 is used.
4. Observe that the Date Published appends AD to the year. Example: John Smith. (05/2021AD) 2021. "Awesome Journal Article…"

Proposed resolution

Bibcite should not display AD after 4-digit years. Bonus for appending AD to two-digit years and adding BC support. I don't think there are many journal articles published earlier than 100AD, but other reference types could benefit from this feature.