[Bug] Time labels are getting rendered on the map as epoch seconds instead of human readable time

**Describe the bug**
Since upgrading from 2.4.0 to the 2.5.5, time labels are now less readable.

**To Reproduce**
Steps to reproduce the behavior:
1. Go https://kepler.gl/demo/earthquakes
2. Add the DateTime (time) column as a label of the point layer

**Expected behavior**
Readable time labels that either correspond to the original text (e.g. `03:12` for hh:mm, or `2021-01-01 03:12` for human readable datetime)

**Screenshots**

Reproduce the issue at https://kepler.gl/demo/earthquakes by adding the DateTime column as a point-layer label, then trace the label formatting path for temporal values. Compare the displayed epoch seconds with the source datetime and verify that the completed change produces readable time or datetime labels without regressing other label types.

Written by the indexing model from the issue text.