feat(packages): Remove arbitrary six-level maximum to list nesting

packages/lists/init.lua

@@ -123,10 +123,7 @@ function package.doNestedList (_, listType, options, content)
    local depth = SILE.settings:get("lists.current." .. listType .. ".depth") + 1
 
    -- styling
-   local enumStyle = styles[listType][depth]
-   if not enumStyle then
-      SU.error("List nesting is too deep")
-   end
+   local enumStyle = styles[listType][(depth - 1) % 6 + 1]
    -- options may override the default styling
    enumStyle = pl.tablex.copy(enumStyle) -- shallow copy for possible overrides
    if enumStyle.display then
@@ -305,8 +302,6 @@ Any other element causes an error to be reported, and any text content is ignore
     \end{itemize}
 \end{itemize}
 
-The current implementation supports up to six indentation levels.
-
 On each level, the indentation is defined by the \autodoc:setting{lists.itemize.leftmargin} setting (defaults to \code{1.5em}) and the bullet is centered in that margin.
 Note that if your document has a paragraph indent enabled at this point, it is also added to the first list level.
 
@@ -335,8 +330,6 @@ The enumeration starts at one, unless you specify the \autodoc:parameter{start=<
     \end{enumerate}
 \end{enumerate}
 
-The current implementation supports up to six indentation levels.
-
 On each level, the indentation is defined by the \autodoc:setting{lists.enumerate.leftmargin} setting (defaults to \code{2em}).
 Note, again, that if your document has a paragraph indent enabled at this point, it is also added to the first list level.