Update LibAV sync scaler to respect `libavOptions`

[jack-guy]

First, thanks for the incredible work on this library!

I've been attempting to use this library in my application through our bundler, which has me supplying LibAV, libAvOptions.factory, and libavOptions.wasmurl manually. I'm getting an error loading this polyfill, however. scalerAsync respects these custom path options, but scalerSync doesn't. This results in an unhandled error. I see this is explicitly the case in the docstring for rendering.load, but I can't think of a good reason for that - it seems that these two LibAV instances should be the same except for the noworker: true option?

Anyway, figured I'd attempt an upstream, if not I will just end up patching this in locally.