Incorrect/Misleading type hint for constructors of RecordingSet/SupervisionSet/CutSet

[csukuangfj]

lhotse/lhotse/audio.py

Lines 960 to 961 in 3c621b5

	def __init__(self, recordings: Mapping[str, Recording] = None) -> None:
	self.recordings = ifnone(recordings, {})

lhotse/lhotse/supervision.py

Lines 542 to 543 in 3c621b5

	def __init__(self, segments: Mapping[str, SupervisionSegment]) -> None:
	self.segments = ifnone(segments, {})

lhotse/lhotse/cut/set.py

Lines 240 to 241 in 3c621b5

	def __init__(self, cuts: Optional[Mapping[str, Cut]] = None) -> None:
	self.cuts = ifnone(cuts, {})

But they actually also accept an iterator/Iterable, see the code below:

lhotse/lhotse/serialization.py

Line 399 in 3c621b5

return cls(LazyManifestIterator(path))

Also, the type hints for RecordingSet/SupervisionSet should use Optional if they accept a None value, like what CutSet is doing.

[csukuangfj]

lhotse/lhotse/lazy.py

Line 196 in 3c621b5

class LazyManifestIterator(ImitatesDict):

I see. LazyManifestIterator acts like a dict. Clever design!