Implement an ApiFile helper for verifying signatures and uploading them, as well as deltas.

[binn]

Also, identify when deltas are required by the API as well.

A weird yet neat way to implement this is to make extension libraries that build onto the VRChat builder, like so builder.WithSignatures() and builder.WithAmazonUploading() to instantiate those two helpers, which the extension libraries will implement, say, an IVRChatS3Uploader and an IVRChatSignatureBroker. These will be used in ApiFile to instantiate and perform those tasks if needed. VRChat.Signatures and VRChat.S3 packages could be downloaded to implement these.