Align C++ names with Python names

[NicolasHug]

Some of the names we use in C++ are slightly different from the ones we expose in Python. Currently the main ones are visible from the metadata:

torchcodec/src/torchcodec/decoders/_core/_metadata.py

Lines 162 to 169 in 9e3a219

	num_frames_from_header=stream_dict.get("numFrames"),
	num_frames_from_content=stream_dict.get("numFramesFromScan"),
	begin_stream_from_content_seconds=stream_dict.get(
	"minPtsSecondsFromScan"
	),
	end_stream_from_content_seconds=stream_dict.get(
	"maxPtsSecondsFromScan"
	),

We should align the C++ names with the Python ones.