Single Stat: allow timestamps to be displayed as the stat

Currently, Single Stat will only render strings or numbers without any interpretation of what they represent. For example, a timestamp in JavaScript is a number that can be interpreted as milliseconds from a certain time.

**Proposal**: Allow Single Stat to interpret numbers as timestamps and render a time rather than a number.

Here is an example .csv that will _not_ show a timestamp, but rather just a number.
```
#group,false,false,true,true,true,true,false,false,true
#datatype,string,long,string,string,dateTime:RFC3339,dateTime:RFC3339,dateTime:RFC3339,dateTime:RFC3339,string
#default,_result,,,,,,,,
,result,table,_field,_measurement,_start,_stop,_time,_value,url
,,0,traefik_config_last_reload_success,prometheus,2021-11-12T17:31:49.314450792Z,2021-11-12T18:31:49.314450792Z,2021-11-12T18:31:02.720095288Z,2021-11-12T14:43:33Z,https://www.google.com

```

The output is this but what we really want is a timestamp:

Start by tracing the Single Stat rendering path and how the CSV data type or timestamp value reaches it. Check where numeric values are formatted, then verify that timestamp-valued numbers render as a time rather than a raw number. Done means the provided timestamp example displays a timestamp in Single Stat without regressing ordinary numeric values.

Written by the indexing model from the issue text.