private List<FSCacheInfo> getExpired(List<FSCacheInfo> recs) {
		long lastUsedCutoffMS = System.currentTimeMillis() - filesystemPurgeDelayMS;
		List<FSCacheInfo> results = new ArrayList<>();
		for (FSCacheInfo fsci : recs) {
			FileSystemRefManager refManager = fsci.ref.getFilesystem().getRefManager();
			long lastUsedTS = refManager.getLastUsedTimestamp();
			if (lastUsedTS < lastUsedCutoffMS) {
				results.add(fsci);
			}
		}
		return results;
	}
Performs maintainence on the filesystem cache, closing() any filesystems
that are not used anymore.
Ghidra/Features/Base/src/main/java/ghidra/formats/gfilesystem/FileSystemInstanceManager.java