ineffecient / incorrect classpath handling

[maxandersen]

I think this is a change after #76 suggested refactor - if not - still an issue :)

jjava/jjava-kernel/src/main/java/org/dflib/jjava/kernel/JavaKernel.java

Line 110 in 79ac72b

paths.forEach(jShell::addToClasspath);

this line is in a method that takes a list of strings that are calling addtoclasspath which is an expensive operation (semi-restart jshell)
and it treats the string as classpath separated by path Seprator.....thats fine - but then iterate those via extension loader as if they are paths to individual paths...

• that latter will fail if actually given a classpath
• this add to path is quite ineffecient to and is also used in maven magics ...so if you add something with lets say 5 dependencies it is noticably slower.

[andrus]

Good catch, my bad. JShell docs are not explicit on what the "path" argument should be (an individual entry or multiple separated entries). But looking at its source code, it appears it would support the latter. So yeah, let me combine multiple calls to just one taking a String separated with File.pathSeparator