private boolean isCacheFileName(String s) {
			return FILENAME_REGEX.matcher(s).matches();
		}
Prunes cache if interval since last maintenance exceeds {@link #MAINT_INTERVAL_MS}
<p>
Only called during construction, and the only known multi-process conflict that can occur
is when re-writing the "lastMaint" timestamp file, which isn't a problem as its the
approximate timestamp of that file that is important, not the contents.

@param cacheDir cache directory location 
@param nestingLevel the depth of directory nesting, 2 for old style, 1 for newer style
@return {@link FileCacheMaintenanceDaemon} instance if started, null otherwise
Ghidra/Features/Base/src/main/java/ghidra/formats/gfilesystem/FileCache.java