fix: handle resolution changes gracefully

[Efe-Cal]

• Changed the preferred MIME type for MediaRecorder from video/mp4;codecs=avc1 to video/mp4;codecs=avc3 as this was causing the main issue (and it was in front of our eyes all this time, on dev tools console).
• Added a resizeVideoSample function that resizes video frames to a target width and height using letterboxing.
• Modified the video concatenation logic to detect when input frames don't match the output dimensions and resize them before adding them to the output.
• The output video dimensions are now set to the maximum width and height found among all input tracks, ensuring no cropping or stretching.

fixes #22
fixes #78