better history suggestions

I think it would be cool if the history suggestions wouldn't just work for full commands but also for sub-commands/strings.

e.g
i run the command clear

in the shell i will get the history suggestion for it, but only if i didnt enter anything else yet.

echo "test"; c will not suggest clear here

this would be especially useful in cases like this:

scp path/to/some/file/ root@123.123.123:~

if someone would want to upload another file, they wouln't get a suggestion for the second part, so root@123.123.123:~ would need to fully by typed out again;

Start by tracing Reedline's history suggestion handling for input containing a command separator, using the examples echo "test"; c and scp path/to/some/file/ root@123.123.123:~ as the target cases. The change is done when history suggestions can match relevant sub-command or argument strings without breaking full-command suggestions; add or update tests alongside the existing history suggestion behavior.