Preprompt and prompt are two distinct concepts in pure: the preprompt is
where the directory and git info live, whereas the prompt (`PROMPT`) is
as pure and simple as `%(?.%F{magenta}.%F{red})❯%f`.
In the `prompt_pure_preprompt_render` function though, prompt and
preprompt are used interchangeably, which makes it confusing the first
time one reads it. (The lines `[[ "${prompt_pure_last_preprompt}" !=
"${prompt}" ]]` and `prompt_pure_last_preprompt=$prompt` perfectly
illustrate the interchangeable use and the potential point of
confusion.)
Therefore, this commits corrects the problem by renaming the `prompt`
local variable to `preprompt`, and updating comments accordingly.
* `prompt_pure_git_delay_dirty_check` holds the (finish) timestamp of
the last dirty check (if the dirty check took more than 2 seconds);
renamed to `prompt_pure_git_last_dirty_check_timestamp`.
* Local variable `dirty_check` holds the elapsed time in seconds since
the last dirty check (if the timestamp is set); renamed to
`time_since_last_dirty_check`.
Zhiming Wang