clippy: clear the workspace errors and apply the machine fixes

- Mark the raw-pointer interop entry points unsafe with # Safety docs
  (oak-core upload/download/frame-from-pixels, oak-audio convert) and
  satisfy the existing callers (tests).
- mut_from_ref: allow with the ABI contract documented (the handle
  get_mut helpers in oak-timeline/oak-render/oak-task take the shared
  reference the C ABI passes; exclusivity is the caller's unsafe
  contract).
- Fix the eq_op in the white-balance normalization (green / green).
- Apply cargo clippy --fix across the workspace (redundant closures and
  field names, field reassignment, items after test modules, ...).
- Revert the replace_box fix in image_effect's clip_define: a
  redefinition must allocate a new box, otherwise the old clip handle
  stays valid and the HS-map replace contract (clip != clip2) breaks.
- 283 warnings remain; they are all non-machine-applicable
  (chunks_exact -> as_chunks needs a manual iter_mut, too_many_arguments,
  complex types, missing Safety docs, ...) and are tracked as the
  follow-up.

crates/oak-node/tests/value_keyframe_test.rs

@@ -70,7 +70,7 @@ fn texture_value_drop_releases() {
 	assert_eq!(refs(&h), 2);
 
 	{
-		let v = NodeValue::Texture(h.clone());
+		let v = NodeValue::Texture(h);
 		assert_eq!(refs(&h), 2, "no extra reference taken on clone");
 		drop(v); // must release the payload's reference
 		assert_eq!(refs(&h), 1);
@@ -97,7 +97,7 @@ fn texture_value_clone_addrefs() {
 	assert_eq!(refs(&h), 1);
 
 	{
-		let a = NodeValue::Texture(h.clone());
+		let a = NodeValue::Texture(h);
 		assert_eq!(refs(&h), 1, "construction takes the caller's reference");
 		{
 			let b = a.clone();