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-render/src/cache.rs

@@ -144,7 +144,7 @@ fn uuid_text_to_bytes(uuid: &str) -> [u8; 16] {
 			break;
 		}
 		let d = c.to_digit(16).unwrap_or(0) as u8;
-		if nibble % 2 == 0 {
+		if nibble.is_multiple_of(2) {
 			bytes[nibble / 2] = d << 4;
 		} else {
 			bytes[nibble / 2] |= d;
@@ -286,7 +286,7 @@ impl PlaybackCache {
 	pub fn set_uuid(&mut self, uuid: &str) {
 		self.uuid = uuid.to_string();
 		let dir = self.disk_dir.clone();
-		let _ = self.load_state(&std::path::Path::new(&dir));
+		let _ = self.load_state(std::path::Path::new(&dir));
 	}
 
 	/// Set the frame timebase (frame-hash flavors; C++ `set_timebase`).
@@ -319,7 +319,7 @@ impl PlaybackCache {
 		self.passthroughs.retain(|(r, _)| !overlaps(*r, range));
 		if self.saving_enabled {
 			let dir = self.disk_dir.clone();
-			let _ = self.save_state(&std::path::Path::new(&dir));
+			let _ = self.save_state(std::path::Path::new(&dir));
 		}
 	}
 
@@ -328,7 +328,7 @@ impl PlaybackCache {
 		self.validated.insert(range);
 		if self.saving_enabled {
 			let dir = self.disk_dir.clone();
-			let _ = self.save_state(&std::path::Path::new(&dir));
+			let _ = self.save_state(std::path::Path::new(&dir));
 		}
 	}
 
@@ -401,7 +401,7 @@ impl PlaybackCache {
 		}
 		if self.saving_enabled {
 			let dir = self.disk_dir.clone();
-			let _ = self.save_state(&std::path::Path::new(&dir));
+			let _ = self.save_state(std::path::Path::new(&dir));
 		}
 	}
 
@@ -421,7 +421,7 @@ impl PlaybackCache {
 		}
 		if self.saving_enabled {
 			let dir = self.disk_dir.clone();
-			let _ = self.save_state(&std::path::Path::new(&dir));
+			let _ = self.save_state(std::path::Path::new(&dir));
 		}
 	}