Extract time helper functions to a separate file

[frm]

If you load the git plugin without exec_time, the following error happens:

prompt_geometry_git_time_since_commit:9: command not found: prompt_geometry_seconds_to_human_time
master :: •

Sample configuration:

GEOMETRY_PROMPT_PLUGINS_PRIMARY=(git)
GEOMETRY_PROMPT_PLUGINS_SECONDARY=(path)

This happens because git depends on functions defined in exec_time. This PR solves this by extracting these functions to a separate lib/time.zsh file.

[frm]

Ping @desyncr @jedahan

[jedahan]

will look at this evening (in ~4 hours)

[jedahan]

thanks for being so patient

[frm]

All good :)