Clarify computation of suite durations

The suite duration table, bucketed by platform, computes shortest and longest suite execution duration, and slowest matrix branch.

Like so:
| longest taken | shortest taken | slowest branch | platform |
|-|-|-|-|
|124 min 42 sec | 117 min 13 sec | kind-v1.32.11-PostgreSQL-18.6 | kind |

The main loop if Ciclops iterates through all test outputs in JSON, recording start times and end times.
This happens in `track_time_taken(test_results, test_times, suite_times):`
It is not until Ciclops has seen all the test outputs that we can compute suite duration, since this is spanned from the start of the first test to execute to the end of the last test to execute.

There is extra logic that gets applied in `format_suite_durations_table`
This should be unnecessary. The `format...` function should simply apply formatting directives and sort the table elements.