improve ban command input

[hyperneutrino]

Summary of Changes

• currently, the ban command only allows inputting a number of days for purging on ban, which is outdated as full second-by-second granularity is now supporter
• additionally, the ban command will currently experience an internal error if the duration provided exceeds the maximum allowance of 7 days instead of offering a descriptive error message
• this change allows inputting any duration and provides a meaningful error message

Steps to Reproduce

• use the ban command

Demonstration of Changes

[davidgan1218]

maybe we should add option to specify ban duration as well as message purging duration.