combinatorics/graycode: Made rank a cached property.
combinatorics/graycode: Made rank a cached property.

Signed-off-by: Saptarshi Mandal <13ec3c7bab52575f3a0cda6406c76269cc13b041@gmail.com>

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