Adds support for the time unit option mentioned in #597.

Some decisions made:

• Uses max latency (slowest request) instead of mean (as in the example in the issue) to automatically determine unit if not provided. The main reason being that mean latency may be an order of magnitude smaller than slowest and therefore you will often get microseconds instead of milliseconds by default.
• Limits TUI view to milliseconds. This is because in microseconds and nanoseconds, the numbers appear as -inf or NaN, and its not really practical anyways to view the last n microseconds or nanoseconds.
• This option is only supported in text summary (similar to the example mentioned in the issue).

I will post some example outputs in the issue thread.