`st.metric` treatment of delta=0

[tilusnet]

Checklist

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Summary

Hi,

I would welcome an additional treatment of delta = 0.

Why?

To avoid showing green "up arrow" zero values, or red "down arrow" zero values which are awkward.

How?

st.metric

• .delta_color(): "normal" (default) - The color is red when the delta is negative, green when positive and grey when zero.
• .delta_arrow(): "auto" (default) - The arrow direction follows the sign of delta, and "-" (or right arrow?) if delta is zero

Additional Context

No response

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[zhangyue325]

Opened PR #15057 to address this issue.