feat(utils): add format_ts

[teaishealthy]

Summary

Create a new function format_ts that can format a unix timestamp, format_dt can use this function too to reduce code duplication.

Closes #1085

This is a Code Change

• I have tested my changes.
• I have updated the documentation to reflect the changes.
• I have run task pyright and fixed the relevant issues.

[spifory]

And also it's not too important but you may want to add a versionchanged to format_dt.

[teaishealthy]

And also it's not too important but you may want to add a versionchanged to format_dt.

@spifory
The external api for format_dt did not change, no reason to.