fix: discard stale Image loads for recycled/re-bound views

[mrousavy]

HybridImageLoader.requestImage(forView:) kicked off an async load and then unconditionally assigned the result to the view's imageView, with no cancellation and no way to tell whether that result was still wanted.

In a list, that means:

1. Cell A starts loading image A into view V.
2. V is recycled and re-bound to cell B, showing image B.
3. Load A resolves and overwrites V with image A.

prepareForRecycle() clearing the image doesn't help, because it runs before the stale completion lands. The same happens without recycling whenever the image prop changes mid-load and the two loads resolve out of order (easy to hit, since a cached HybridImageLoader resolves instantly while an uncached one doesn't).

This adds a monotonic per-view request token:

• beginImageRequest() starts a request and invalidates any in-flight one
• cancelImageRequest() invalidates without starting a new one (called from dropImage)
• isImageRequestValid(token) is checked right before the result is applied

On iOS this is exposed as a new ImageRequestTracking protocol next to NativeImageView, so third-party image views can opt into it. Views that don't conform keep working exactly as before, they just don't get cancellation.

react-native-nitro-web-image is unaffected - SDWebImage and Coil already scope requests to the target view.

Testing

Not verified on device - CI builds cover compilation.