support #[patch(skip_wrap, apply_by(fn))]

README.md

@@ -191,7 +191,7 @@ Two attribute namespaces are provided for the catalyst feature because we need t
 - `#[patch(attribute(derive(...)))]`: add derives to the field in the generated patch struct.
 - `#[patch(empty_value = ...)]`: define a value as empty, so the corresponding field of the patch will not be wrapped by `Option`, and the patch is applied when the field differs from the empty value.
 - `#[patch(skip_wrap)]`: keep the field type as-is in the patch struct (no extra `Option` wrapping). Useful when the field is already `Option<...>` (for example `Option<Vec<_>>`) and you do not want a double-`Option` in the patch. With `skip_wrap`, `None` in the patch means "no change" and `Some(v)` sets the field to `Some(v)` (including `Some(vec![])` to clear the vector). Cannot be combined with `empty_value`.
-- `#[patch(apply_by(fn))]`: call `fn(original, new_value)` to update the field when the patch field is `Some`, instead of a plain assignment. The function signature must be `fn(original: &mut T, new_value: T)` — it mutates in place, so no `Default` bound is needed. When two patches are combined with `+` and both carry `Some` for this field, the same function merges the two patch values.
+- `#[patch(apply_by(fn))]`: call `fn(original, new_value)` to update the field when the patch field is `Some`, instead of a plain assignment. The function signature must be `fn(original: &mut T, new_value: T)` — it mutates in place, so no `Default` bound is needed. When two patches are combined with `+` and both carry `Some` for this field, the same function merges the two patch values. Can be combined with `skip_wrap` as `#[patch(skip_wrap, apply_by(fn))]`: the field type is kept as-is (no extra `Option` wrapping) and `fn` is called to apply the change.
 - `#[patch(nesting)]`: treat the field as a nested patchable struct. The inner struct must also derive `Patch`. Requires the `nesting` feature.
 - `#[patch(addable)]`: allow conflicting patches to add their values together with the `+` operator instead of panicking. Requires the `op` feature.
 - `#[patch(add = fn)]`: like `addable`, but use the specified function to combine values. Requires the `op` feature.