Zig is still under active development, and new releases often introduce
breaking changes. This makes updating the default version of zig easier.
Some packages did not receive this change because they could be using
the c compiler or linker of zig, which doesn't receive as much breaking
changes compared to e.g. the zig std library.
https://github.com/NixOS/nixpkgs/pull/248243#discussion_r1289401340
also updates nixdoc to 2.3.0. the nixdoc update is not a separate commit
because that would leave the manual build broken for one commit,
potentially breaking bisects and rebases.
skipping heading levels (eg from # to ###, or starting at ###) is legal
in pandoc, but not in nixos-render-docs. pandoc acts as though section
levels *were* consecutive, nixos-render-docs prefers to tell people not
to do that kind of thing because it can make documents more fragile.
pandoc drops .title classes when rendering to docbook, so these are
effectively just paragraphs anyway. without support for including them
in a table of contents the complexity of parsing them in
nixos-render-docs won't be warranted.
