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/src/project.rs

@@ -347,8 +347,8 @@ impl Project {
 					return self.custom_cache_path.clone();
 				}
 			}
-			1 => {
-				if !self.filename.is_empty() {
+			1
+				if !self.filename.is_empty() => {
 					let dir = std::path::Path::new(&self.filename)
 						.parent()
 						.map(|p| p.to_string_lossy().into_owned())
@@ -357,7 +357,6 @@ impl Project {
 						return format!("{}/cache", dir);
 					}
 				}
-			}
 			_ => {}
 		}
 		// Default location: the shared disk-cache directory (single-lib: