Source discovery for cljs/cljc files in a deps.edn project. Reuses
`skeptic.cli.paths/discover-paths` to obtain the project's resolved
source paths from `clojure.tools.deps/create-basis`, then walks them
for cljs/cljc files. `discover-paths` returns paths verbatim from the
deps.edn (relative strings like "src"); they are absolutized against
`root` here before walking.

Walk a collection of source roots and partition the matching files into
cljs and cljc buckets. Paths that do not exist are skipped silently;
paths that point at a regular file are included if their extension matches.

Source discovery for cljs/cljc files in a Leiningen project. Reads
:source-paths and :test-paths from the project map, plus any cljsbuild
build :source-paths if present, and walks them for cljs/cljc files.

Source discovery for cljs/cljc files in a shadow-cljs project. Reads
shadow-cljs.edn at `root` as plain EDN and walks the top-level
:source-paths key for cljs/cljc files.