Remove unnecessary Send + Sync bounds from Redaction (#874)

## Summary

Follow-up to #873 ("Don't use `Arc` in `Settings` unnecessarily").

- Remove `Send + Sync` bounds from `Redaction::Dynamic` variant
- Remove `Send + Sync` bounds from `dynamic_redaction()` function
- Remove `Send + Sync` bounds from `Settings::add_dynamic_redaction()`
method

Since `Settings` are stored in thread-local storage and wrapped in `Rc`,
they can never cross thread boundaries. The `Send + Sync` bounds were
vestigial from when `Arc` was used for `DEFAULT_SETTINGS`.

This relaxes the API to allow non-`Send` closures in dynamic redactions,
which is now safe since those closures can never be sent to another
thread.

## Test plan

- [x] All tests pass with `cargo test --all-features`
- [x] No clippy warnings

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: max-sixty

.gitignore

@@ -12,4 +12,4 @@ WORKSPACE.bazel
 bazel-*
 
 # Emacs backups
-*~
+*~

insta/src/redaction.rs

@@ -54,7 +54,7 @@ pub enum Redaction {
     /// Static redaction with new content.
     Static(Content),
     /// Redaction with new content.
-    Dynamic(Box<dyn Fn(Content, ContentPath<'_>) -> Content + Sync + Send>),
+    Dynamic(Box<dyn Fn(Content, ContentPath<'_>) -> Content>),
 }
 
 macro_rules! impl_from {
@@ -127,7 +127,7 @@ impl<'a> From<&'a [u8]> for Redaction {
 pub fn dynamic_redaction<I, F>(func: F) -> Redaction
 where
     I: Into<Content>,
-    F: Fn(Content, ContentPath<'_>) -> I + Send + Sync + 'static,
+    F: Fn(Content, ContentPath<'_>) -> I + 'static,
 {
     Redaction::Dynamic(Box::new(move |c, p| func(c, p).into()))
 }

insta/src/settings.rs

@@ -413,7 +413,7 @@ impl Settings {
     pub fn add_dynamic_redaction<I, F>(&mut self, selector: &str, func: F)
     where
         I: Into<Content>,
-        F: Fn(Content, ContentPath<'_>) -> I + Send + Sync + 'static,
+        F: Fn(Content, ContentPath<'_>) -> I + 'static,
     {
         self.add_redaction(selector, dynamic_redaction(func));
     }