Fix some media bugs & support big video file

[canwdev]

• Fix: addMediaDefinition ext and cover
• Support big video files: demo

slide.addMedia({
	x: 1.0,
	y: 2.2,
	w: imgWidth,
	h: imgHeight,
	type: "video",
	path: videoUrl,
	ext: "mp4", // fix file extension name, Sometimes the url does not contain the suffix name
	cover: imgData.base64, // video cover base64 string
	isFsPath: true, // Let node.js read the file directly instead of converting to base64
});

// Use stream output directly
const fileData = await pptx.stream({
	compression: false,
});
console.log("createWriteStream...");
const out = fs.createWriteStream(savePath);
fileData.pipe(out).on("finish", () => {
	console.log("Success!");
});

[gitbrent]

Thanks @canwdev !