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-plugin/src/render.rs

@@ -108,7 +108,7 @@ pub fn texture_create(
 		return Err(Error::Invalid);
 	}
 	// 行跨度推导通道数（RGB 3 通道等非常规分量）。
-	if linesize > 0 && w > 0 && (linesize as usize) % (w * bpc) == 0 {
+	if linesize > 0 && w > 0 && (linesize as usize).is_multiple_of(w * bpc) {
 		frame.channels = (linesize as usize / (w * bpc)) as i32;
 	}
 	let tight = frame.linesize_bytes();