Fix crash in tracking spring animations when toValue node is detached

[kmsbernard]

Summary:

This PR fixes an Android Native Animated crash in tracking + spring animations when the tracked toValue node is detached.

In TrackingAnimatedNode.update, if the tracked node could not be resolved, we used to write toValue = null into animationConfig. SpringAnimation.resetConfig expects toValue to be a number, so this could crash with NullPointerException: null cannot be cast to non-null type kotlin.Number

This can happen in real apps during graph teardown (for example unmount/re-render/navigation transitions), where tracking may still update for a transient frame after the tracked node has been detached.

Fix:

• Do not propagate null toValue from TrackingAnimatedNode.
• If the tracked node is missing, fallback to the driven value node’s current value.
• If both nodes are unavailable, return safely.

This PR also adds a regression test.

Changelog:

[ANDROID] [FIXED] - Prevent Native Animated tracking spring crash when tracked toValue node is detached.

Test Plan:

Added regression test NativeAnimatedNodeTraversalTest.testTrackingSpringDoesNotCrashWhenToValueNodeIsDetached

• On a test-only commit (without the fix), the new test fails with: NullPointerException: null cannot be cast to non-null type kotlin.Number
• On this PR (with the fix), test pass.