Kills seconds_per_tick from status effect tick, replaces it with seconds_between_ticks to clarify some things (#77219)

## About The Pull Request

https://github.com/tgstation/tgstation/pull/66573#discussion_r861157216

`status_effect/proc/tick(seconds_per_tick)` is wildly misleading and I
feel like I should address it

For a majority of status effects, they process on fast processing but do
not tick every fastprocessing tick

This means that using `seconds_per_tick` here is not giving you the
seconds between status effect ticks, it's giving you seconds between
processing ticks (`0.2`)

This is how it's misleading - If you have a tick interval of `1
SECONDS`, you'd think `seconds_per_tick` is, well, one. But it's
actually one-fifth. So all of your effects are now 80% weaker.

I have replaced the use of `seconds_per_tick` in tick with
`seconds_between_ticks`.

This number is, quite simply, the initial tick interval of the status
effect divided by ten.

An effect with the tick interval of `1 SECONDS` has a
`seconds_between_ticks` of 1.

As a consequence, some things which were inadvertently made weaker, such
as fire and some heretic things (at a glance), are now a little
stronger.

## Why It's Good For The Game

See above. Makes it more clear what you're doing when working with
effects.

## Changelog

🆑 Melbert
code: Updated some status effect tick code to be more clear of how long
is elapsing between ticks. Some effects that were inadvertently weakened
are now stronger as a result (fire and some heretic effects).
/🆑

code/modules/unit_tests/_unit_tests.dm

@@ -102,6 +102,7 @@
 #include "blindness.dm"
 #include "bloody_footprints.dm"
 #include "breath.dm"
+#include "burning.dm"
 #include "cable_powernets.dm"
 #include "card_mismatch.dm"
 #include "cardboard_cutouts.dm"
@@ -233,6 +234,7 @@
 #include "spritesheets.dm"
 #include "stack_singular_name.dm"
 #include "station_trait_tests.dm"
+#include "status_effect_ticks.dm"
 #include "stomach.dm"
 #include "strange_reagent.dm"
 #include "strippable.dm"