Add further READONLY_TOOLS

I foresee this list growing significantly.

Some other tools that would be good to have in the READONLY_TOOLS list

wc # wordcount
jq # json query
yq # but not if the -i Inplace flag is given!
test
realpath
sleep
df
du

For each tool, we should ensure that there are no arguments to the tool that allow it to write to disk/mutate state, and if there is, ensure that argument is excluded from readonly if possible, or otherwise leave that tool out explicitly, with a comment in the sourcecode on why the tool wasn't included.