[3/5] cache cleanup, hadle only immutable objects
[3/5] cache cleanup, hadle only immutable objects

Now we've killed cacheit_fast, we have the only one usable cache_it_immutable,
and let's rename it to just `cacheit`

This patch touches only cache.py internals. I'll convert the rest of sympy in
the following commit.

shikil/sympy,mcdaniel67/sympy,kaushik94/sympy,farhaanbukhsh/sympy,jamesblunt/sympy,tovrstra/sympy,jerli/sympy,jaimahajan1997/sympy,sampadsaha5/sympy,beni55/sympy,wanglongqi/sympy,Gadal/sympy,sunny94/temp,MechCoder/sympy,iamutkarshtiwari/sympy,kmacinnis/sympy,atreyv/sympy,Titan-C/sympy,amitjamadagni/sympy,asm666/sympy,ahhda/sympy,saurabhjn76/sympy,ahhda/sympy,fperez/sympy,kaushik94/sympy,dqnykamp/sympy,atsao72/sympy,emon10005/sympy,Sumith1896/sympy,cswiercz/sympy,atsao72/sympy,minrk/sympy,Mitchkoens/sympy,kmacinnis/sympy,sunny94/temp,jamesblunt/sympy,wanglongqi/sympy,yashsharan/sympy,asm666/sympy,aktech/sympy,ga7g08/sympy,bukzor/sympy,Vishluck/sympy,moble/sympy,wyom/sympy,pandeyadarsh/sympy,pbrady/sympy,abloomston/sympy,hargup/sympy,kaichogami/sympy,postvakje/sympy,kmacinnis/sympy,Curious72/sympy,ryanGT/sympy,kevalds51/sympy,hrashk/sympy,abhiii5459/sympy,atreyv/sympy,ga7g08/sympy,aktech/sympy,rahuldan/sympy,Davidjohnwilson/sympy,maniteja123/sympy,liangjiaxing/sympy,asm666/sympy,flacjacket/sympy,meghana1995/sympy,souravsingh/sympy,ChristinaZografou/sympy,bukzor/sympy,cccfran/sympy,atreyv/sympy,kumarkrishna/sympy,lindsayad/sympy,toolforger/sympy,garvitr/sympy,AkademieOlympia/sympy,Shaswat27/sympy,skidzo/sympy,MridulS/sympy,postvakje/sympy,wyom/sympy,debugger22/sympy,Vishluck/sympy,hrashk/sympy,wyom/sympy,sampadsaha5/sympy,jbbskinny/sympy,beni55/sympy,jbaayen/sympy,toolforger/sympy,kaichogami/sympy,atsao72/sympy,vipulroxx/sympy,postvakje/sympy,shipci/sympy,yashsharan/sympy,madan96/sympy,Designist/sympy,Titan-C/sympy,AunShiLord/sympy,Davidjohnwilson/sympy,sahilshekhawat/sympy,pbrady/sympy,shipci/sympy,emon10005/sympy,lidavidm/sympy,bukzor/sympy,sahmed95/sympy,Shaswat27/sympy,kumarkrishna/sympy,liangjiaxing/sympy,jerli/sympy,cswiercz/sympy,yukoba/sympy,drufat/sympy,vipulroxx/sympy,ga7g08/sympy,mcdaniel67/sympy,sahmed95/sympy,Designist/sympy,farhaanbukhsh/sympy,debugger22/sympy,maniteja123/sympy,hargup/sympy,MechCoder/sympy,moble/sympy,abloomston/sympy,Shaswat27/sympy,mafiya69/sympy,jaimahajan1997/sympy,sunny94/temp,kevalds51/sympy,chaffra/sympy,Curious72/sympy,ChristinaZografou/sympy,Arafatk/sympy,toolforger/sympy,aktech/sympy,abloomston/sympy,Davidjohnwilson/sympy,grevutiu-gabriel/sympy,yashsharan/sympy,ahhda/sympy,MridulS/sympy,lidavidm/sympy,iamutkarshtiwari/sympy,pandeyadarsh/sympy,garvitr/sympy,yukoba/sympy,shipci/sympy,hazelnusse/sympy-old,Sumith1896/sympy,drufat/sympy,Arafatk/sympy,chaffra/sympy,liangjiaxing/sympy,MridulS/sympy,Gadal/sympy,madan96/sympy,iamutkarshtiwari/sympy,pandeyadarsh/sympy,sampadsaha5/sympy,sahilshekhawat/sympy,lindsayad/sympy,shikil/sympy,saurabhjn76/sympy,mafiya69/sympy,dqnykamp/sympy,skirpichev/omg,Arafatk/sympy,pbrady/sympy,AunShiLord/sympy,mafiya69/sympy,garvitr/sympy,Designist/sympy,skidzo/sympy,vipulroxx/sympy,mattpap/sympy-polys,VaibhavAgarwalVA/sympy,skidzo/sympy,cccfran/sympy,wanglongqi/sympy,kaichogami/sympy,rahuldan/sympy,srjoglekar246/sympy,jaimahajan1997/sympy,Vishluck/sympy,lidavidm/sympy,souravsingh/sympy,jbbskinny/sympy,cccfran/sympy,grevutiu-gabriel/sympy,Gadal/sympy,oliverlee/sympy,moble/sympy,jamesblunt/sympy,MechCoder/sympy,madan96/sympy,chaffra/sympy,shikil/sympy,KevinGoodsell/sympy,kevalds51/sympy,kumarkrishna/sympy,yukoba/sympy,AunShiLord/sympy,AkademieOlympia/sympy,souravsingh/sympy,meghana1995/sympy,pernici/sympy,oliverlee/sympy,hazelnusse/sympy-old,maniteja123/sympy,hrashk/sympy,ChristinaZografou/sympy,farhaanbukhsh/sympy,lindsayad/sympy,beni55/sympy,dqnykamp/sympy,emon10005/sympy,cswiercz/sympy,rahuldan/sympy,kaushik94/sympy,diofant/diofant,Mitchkoens/sympy,amitjamadagni/sympy,abhiii5459/sympy,minrk/sympy,Mitchkoens/sympy,Sumith1896/sympy,AkademieOlympia/sympy,grevutiu-gabriel/sympy,sahilshekhawat/sympy,drufat/sympy,VaibhavAgarwalVA/sympy,meghana1995/sympy,hargup/sympy,mcdaniel67/sympy,sahmed95/sympy,VaibhavAgarwalVA/sympy,saurabhjn76/sympy,jbbskinny/sympy,debugger22/sympy,Titan-C/sympy,Curious72/sympy,jerli/sympy,oliverlee/sympy,abhiii5459/sympy