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-codec/src/timecodemetadata.rs

@@ -66,7 +66,7 @@ fn frame_rate(timebase: &Rational) -> f64 {
 /// `drop_frame` is true when the (already trimmed) string contains a `;`.
 /// Returns `None` on any parse failure.
 fn timecode_to_time(timecode: &str, timebase: &Rational, drop_frame: bool) -> Option<Rational> {
-	let mut tokens: Vec<&str> = timecode.split(|c| c == ':' || c == ';').collect();
+	let mut tokens: Vec<&str> = timecode.split([':', ';']).collect();
 	let element_count = 4;
 
 	// Keep only the leading `HH:MM:SS:FF` tokens.