Settings for easylist and itemize

For easylist, I do not use it, so I don't know. With enumitem, you just have to specify an empty label:

documentclass[a4paper,12pt,twoside]{book}
usepackage[a4paper,top=2.5cm,bottom=2.5cm,margin=2.5cm,bindingoffset=0.5cm]{geometry}
usepackage{indentfirst} % indent first paragraph after section
renewcommand{baselinestretch}{1.5}
setcounter{secnumdepth}{6}

makeatletter
deftoclevel@subsubparagraph{6}
providecommandtheHsubsubparagraph {theHsubparagraph.arabic{subsubparagraph}}
newcounter {subsubparagraph}[subparagraph]
renewcommandthesubsubparagraph {thesubparagraph.@arabicc@subsubparagraph}
newcommand*l@subsubparagraph{@dottedtocline{6}{12em}{6em}}
newcommandsubsubparagraph{@startsection{subsubparagraph}{6}{parindent}%
                                       {3.25ex @plus1ex @minus .2ex}%
                                       {-1em}%
                                      {normalfontnormalsizeitshape}}
makeatother

usepackage{enumitem}
renewlist{itemize}{itemize}{9}
setlist[itemize]{noitemsep, topsep=0pt}
setlist[itemize,1]{label=textbullet}
setlist[itemize,2]{label=textendash}
setlist[itemize,3]{label=*}
setlist[itemize,4]{label=·}
setlist[itemize,5]{label =}

usepackage[bidi=basic, layout=lists. tabular]{babel}
babelfont[english]{rm}{Times New Roman}

begin{document}%

begin{itemize}
  item Such subject is:
begin{itemize}
  item rigid-bo:
begin{itemize}
  item mics:
begin{itemize}
 item forces:
  item bodies:
begin{itemize}
 item errer:
end{itemize}
end{itemize}
end{itemize}
end{itemize}
end{itemize}

end{document} 

Regarding the addition of more levels through the use of easlist package, I came across the answer posted by u/Zephyron51 in r/latex
https://www.reddit.com/r/LaTeX/comments/3dgcm5/easylist_levels_not_going_past_4/ Source code can be found in https://pastebin.com/bNqEUrvx

The code can be modified as follows:

documentclass[a4paper,12pt,twoside]{book}
usepackage[a4paper,top=2.5cm,bottom=2.5cm,margin=2.5cm,bindingoffset=0.5cm]{geometry} 
usepackage{indentfirst} 
renewcommand{baselinestretch}{1.5} 
setcounter{secnumdepth}{6} 

makeatletter 
deftoclevel@subsubparagraph{6}
providecommandtheHsubsubparagraph {theHsubparagraph.arabic{subsubparagraph}}
newcounter {subsubparagraph}[subparagraph]
renewcommandthesubsubparagraph {thesubparagraph.@arabicc@subsubparagraph}
newcommand*l@subsubparagraph{@dottedtocline{6}{12em}{6em}}
newcommandsubsubparagraph{@startsection{subsubparagraph}{6}{parindent}%
                                       {3.25ex @plus1ex @minus .2ex}%
                                       {-1em}%
                                      {normalfontnormalsizeitshape}}
makeatother

usepackage{enumitem}
renewlist{itemize}{itemize}{9}
setlistdepth{9}
setlist[itemize]{noitemsep, topsep=0pt}
setlist[itemize,1]{label=textbullet}
setlist[itemize,2]{label=textendash}
setlist[itemize,3]{label=*}
setlist[itemize,4]{label=·}
setlist[itemize,5]{label =}


usepackage[at]{easylist} 
        ListProperties(
                Progressive*=3ex,
                Space=5pt,
                Space*=5pt,
                Style1*=textbullet  ,
                Style2*=begin{normalfont}begin{bfseries}textendashend{bfseries}end{normalfont}   ,
                Style3*=textasteriskcentered  ,
                Style4*=textperiodcentered  ,
                Style5*=textbullet  ,
                Style6*=begin{normalfont}begin{bfseries}textendashend{bfseries}end{normalfont}  ,
                Style7*=textasteriskcentered  ,
                Style8*=textperiodcentered  ,
                Hide1=1,
                Hide2=2,
                Hide3=3,
                Hide4=4,
                Hide5=5,
                Hide6=6,
                Hide7=7,
                Hide8=8 )


usepackage[bidi=basic,layout=lists.tabular]{babel}
babelfont[english]{rm}{Times New Roman}

begin{document}

 begin{easylist}
ListProperties(Space1=0.1cm, % Level not 1, Space1,  Level 1
                Space1*=0.1cm,% Level 1,     Space1*, Level 1
                Space2=0.15cm,    % Level not 2, Space2,  Level 2
                Space2*=0.1cm, % Level 2,     Space2*, Level 2
                Space3=0.1cm, % Level not 3, Space3,  Level 3
                Space3*=0.1cm, % Level 3,     Space3*, Level 3
                )
@ Such subject is:
@@ rigid-bo:
   @@@ mics: 
   @@@@  bodies:
   @@@@@  forces:
    @@@@@@ errer:
    @@@@@@@ errer:
    @@@@@@@@ errer: 
end{easylist}
end{document}
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[![Output][1]][1]


  [1]: https://i.stack.imgur.com/tGGie.jpg