Add unit property and as_unit method to Timestamp, Timedelta and NaTType
#2256
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| 15s | |
| 3m 0s | |
| 3m 4s | |
| 2m 58s | |
| 3m 12s | |
| 4m 57s | |
| 5m 14s | |
| 5m 15s | |
| 5m 45s | |
| 3m 19s | |
| 3m 26s | |
| 7m 16s | |
| 5m 10s | |
| 52m 51s |