Fix nested subdirectory listing #1430

[Kirill888]

Walking up the directory tree never went higher than one directory up:

For example A/B/C, would register A/B/C -> A/B, but not A/B -> A, due to this line

filesystem_spec/fsspec/implementations/reference.py

Lines 994 to 996 in 1637a97

	self.dircache.setdefault(
	par0.rsplit("/", 1)[0] if "/" in par0 else "", []
	).append({"name": par0, "type": "directory", "size": 0})

The solution is to first collect all the newly observed sub-directories, and only then update dircache with new directory entries.

• Closes Missing sub-directories when listing root in ReferenceFileSystem #1430