Inconsistent processing length when end/duration is set as frames (CLI-only)

[Breakthrough]

[PySceneDetect] PySceneDetect 0.6.2
[PySceneDetect] Downscale factor set to 5, effective resolution: 256 x 108
[PySceneDetect] Detecting scenes...
Detected: 0 | Progress:  90%|███████████████████████████████████████████████████▎     | 9/10 [00:00<00:00, 346.18frames/s] 
[PySceneDetect] Processed 9 frames in 0.0 seconds (average 300.01 FPS).
[PySceneDetect] Detected 1 scenes, average shot length 0.4 seconds.

May be related to the fixes made for #307. End time should be exclusive, so setting -e 10 should stop after processing 10 frames, e.g. the correct output here should be 10/10. This also affects the output for time arguments --duration and --end. For example if time --end 10 is specified, the last frame that will be processed is actually frame 9.

With --duration this happens inconsistently. If no start time is specified, 9 frames are processed. However if start time is set to frame 2, it actually stops processing at frame 10. When setting start/duration/end as frames, this should be reflected in the output correctly. This does mean that when specifying time values as frame numbers, they will be treated differently, but this should lead to more expected behaviour.

The following changes will be made but will ONLY affect specifying times as exact number of frames (using timecodes or seconds is unaffected):

• start as frame number excludes presentation time
• end and duration as frame number should include presentation time
• duration as frames should process exactly that amount of frames
• end - start should process (1 + end - start) frames, such that setting start == end still processes a single frame
• end as frame number should be inclusive and indicate the last frame to process (currently it excludes presentation time and stops at the end of the previous frame)
• duration as frame number should stop at frame (start + duration - 1)
• progress bar should match exact amount of frames being processed (e.g. same as duration or end - start)