fix(fs): close directory file descriptor

[andrewazores]

Related to https://github.com/cryostatio/cryostat/issues/1444

The FileSystem wrapper around java.nio.file.Files fails to close the Stream<Path> it opens when listing directory contents. This class is dependency-injected in Cryostat (for testing mock ease) and used in several frequently called codepaths. This leaking fd adds up quite quickly as Cryostat runs and serves requests.

To test/verify, try the following:

$ sh smoketest.sh # in first terminal
$ podman ps --ns # in second terminal here and next commands. Note the PID of the cryostat container
$ watch 'ls -l /proc/$pid/fd | wc -l' # replace $pid with the PID from above
$ xdg-open https://localhost:8181 # click around the UI, particularly click back and forth between Recordings, Archives, and other clientside views. Watch the open fd count in the second terminal grow

Then check out this PR, mvn install it, update the Cryostat pom.xml to use the updated -core, rebuild the container and re-run the test. There is another fd leak (I think in the Cryostat server-side code, checking on it still) that grows much more slowly, but with this leak fixed the number should grow much more slowly than previously.

[tthvo]

Looks good! Fixed the issue!