fix!: useRiveFile error is now Error, riveFile undefined while loading

Align useRiveFile with useViewModelInstance semantics: riveFile is
undefined while loading (was null), error is Error object (was string).
isLoading kept for convenience. Memoize error in useViewModelInstance,
accept undefined source to avoid ?? null at call sites.

Author: mfazekas

example/src/demos/DataBindingArtboardsExample.tsx

@@ -62,7 +62,7 @@ export default function DataBindingArtboardsExample() {
     return (
       <View style={styles.container}>
         <Text style={styles.errorText}>
-          {error || 'Failed to load Rive files'}
+          {error?.message || 'Failed to load Rive files'}
         </Text>
       </View>
     );

example/src/exercisers/FontFallbackExample.tsx

@@ -258,7 +258,7 @@ function MountedView({ text }: { text: string }) {
     // https://rive.app/marketplace/26480-49641-simple-test-text-property/
     require('../../assets/rive/font_fallback.riv')
   );
-  const { instance } = useViewModelInstance(riveFile ?? null);
+  const { instance } = useViewModelInstance(riveFile);
 
   const { setValue: setRiveText, error: textError } = useRiveString(
     TEXT_PROPERTY,
@@ -285,7 +285,9 @@ function MountedView({ text }: { text: string }) {
   if (error || !riveFile) {
     return (
       <View style={styles.riveContainer}>
-        <Text style={styles.errorText}>{error || 'Failed to load file'}</Text>
+        <Text style={styles.errorText}>
+          {error?.message || 'Failed to load file'}
+        </Text>
       </View>
     );
   }

example/src/exercisers/MenuListExample.tsx

@@ -32,7 +32,9 @@ export default function MenuListExample() {
       ) : riveFile ? (
         <MenuList file={riveFile} />
       ) : (
-        <Text style={styles.errorText}>{error || 'Unexpected error'}</Text>
+        <Text style={styles.errorText}>
+          {error?.message || 'Unexpected error'}
+        </Text>
       )}
     </View>
   );

example/src/exercisers/NestedViewModelExample.tsx

@@ -31,7 +31,9 @@ export default function NestedViewModelExample() {
       ) : riveFile ? (
         <WithViewModelSetup file={riveFile} />
       ) : (
-        <Text style={styles.errorText}>{error || 'Unexpected error'}</Text>
+        <Text style={styles.errorText}>
+          {error?.message || 'Unexpected error'}
+        </Text>
       )}
     </View>
   );

example/src/exercisers/OutOfBandAssets.tsx

@@ -49,10 +49,10 @@ export default function OutOfBandAssetsExample() {
 
   if (isLoading) {
     return <ActivityIndicator />;
-  } else if (error != null) {
+  } else if (error) {
     return (
       <View style={styles.safeAreaViewContainer}>
-        <Text>Error loading Rive file</Text>
+        <Text>Error loading Rive file: {error.message}</Text>
       </View>
     );
   }

example/src/exercisers/OutOfBandAssetsWithSuspense.tsx

@@ -102,10 +102,10 @@ function RiveContent({ imageUrl }: { imageUrl: ImageURLS }) {
 
   if (isLoading) {
     return <ActivityIndicator />;
-  } else if (error != null) {
+  } else if (error) {
     return (
       <View style={styles.safeAreaViewContainer}>
-        <Text>Error loading Rive file: {error}</Text>
+        <Text>Error loading Rive file: {error.message}</Text>
       </View>
     );
   }

example/src/exercisers/ResponsiveLayouts.tsx

@@ -46,7 +46,7 @@ export default function ResponsiveLayoutsExample() {
       {isLoading ? (
         <ActivityIndicator size="large" color="#0000ff" />
       ) : error ? (
-        <Text style={styles.errorText}>{error}</Text>
+        <Text style={styles.errorText}>{error.message}</Text>
       ) : riveFile ? (
         <RiveView
           hybridRef={{ f: (ref) => (riveRef.current = ref) }}

example/src/exercisers/RiveDataBindingExample.tsx

@@ -27,7 +27,9 @@ export default function WithRiveFile() {
         ) : riveFile ? (
           <WithViewModelSetup file={riveFile} />
         ) : (
-          <Text style={styles.errorText}>{error || 'Unexpected error'}</Text>
+          <Text style={styles.errorText}>
+            {error?.message || 'Unexpected error'}
+          </Text>
         )}
       </View>
     </View>

example/src/exercisers/RiveDataBindingExampleExpApi.tsx

@@ -26,7 +26,9 @@ export default function WithRiveFile() {
         ) : riveFile ? (
           <WithViewModelSetup file={riveFile} />
         ) : (
-          <Text style={styles.errorText}>{error || 'Unexpected error'}</Text>
+          <Text style={styles.errorText}>
+            {error?.message || 'Unexpected error'}
+          </Text>
         )}
       </View>
     </View>

example/src/exercisers/RiveEventsExample.tsx

@@ -50,7 +50,7 @@ export default function EventsExample() {
         {isLoading ? (
           <ActivityIndicator size="large" color="#0000ff" />
         ) : error ? (
-          <Text style={styles.errorText}>{error}</Text>
+          <Text style={styles.errorText}>{error.message}</Text>
         ) : riveFile ? (
           <RiveView
             style={styles.rive}