[Magiclysm] Make "Concentration" independent, not relying directly on Focus

# Is your feature request related to a problem? Please describe.

Untying "Concentration" from being directly based on Focus.
Optionally making it a new character parameter not tied to Focus.
As it stands now a few minutes of driving or less than a minute of being in melee makes it near-impossible to use spells with "concentration" component.
It's particularly glaring for some quick-cast spells like Magus' teleport of Techno's Hologram that sounds like escape measure but can't be used as such in almost all cases.

Full-on mages might consider disabling learning all skills once they are able to mostly focus on magic but most characters are in practice locked out from using those spells.

# Describe the solution you'd like

Simple option:
_Could code it in myself after @KorGgenT's approval_
(Maybe could be merged into master, since it wouldn't touch any strings?)
Calculate it on the run, make basic value based on Intelligence
It could be lowered be pain, sleepiness, to a small extent weariness, low mood and lost Focus

Extended option:
Make it a new parameter calculated and capped as stated above
It could be consumed by casting spells with concentration requirement and restored during rest and sleep

In future if there will be spells with unlimited duration (you activate them, then deactivate manually) and passive costs (penalty to max Mana, Mana Drain) concentration could be used to cap those (how much effects you can maintain at once)
I think that adding spells with flexible duration would be great extension to current buff spells
Could be also used to make Animist's summon permanent but capped by Concentration so having a horde makes you incapable of concentrating on other spells, but allowing having a horde in the first place

# Describe alternatives you've considered

Having players disable learning of all skills if they plan to use magic in near future or don't even learn those spells

The issue names no files, tests, or entry points. First clarify whether Concentration should be a derived value or a new persistent character parameter, including its effects and recovery rules. Done means an agreed design is implemented and verified for the affected concentration spells.

Written by the indexing model from the issue text.