Replace crossbeam channel with std::sync::mpsc (#861)

* Replace crossbeam channel with std::sync::mpsc

- Replace all uses of crossbeam::channel with std::sync::mpsc
- Remove crossbeam dependency from all Cargo.toml files
- Update documentation to remove crossbeam references
- Use std::sync::mpsc::channel() instead of crossbeam::channel::unbounded()

Fixes #828

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

Co-Authored-By: Claude <noreply@anthropic.com>

* Update mod.rs

---------

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

src/lib.rs

@@ -25,7 +25,6 @@ pub extern crate parry3d as parry;
 #[cfg(all(feature = "dim3", feature = "f64"))]
 pub extern crate parry3d_f64 as parry;
 
-pub extern crate crossbeam;
 pub extern crate nalgebra as na;
 #[cfg(feature = "serde-serialize")]
 #[macro_use]

src/pipeline/event_handler.rs

@@ -1,7 +1,7 @@
 use crate::dynamics::RigidBodySet;
 use crate::geometry::{ColliderSet, CollisionEvent, ContactForceEvent, ContactPair};
 use crate::math::Real;
-use crossbeam::channel::Sender;
+use std::sync::mpsc::Sender;
 
 bitflags::bitflags! {
     #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
@@ -90,14 +90,14 @@ impl EventHandler for () {
     }
 }
 
-/// A collision event handler that collects events into a crossbeam channel.
+/// A collision event handler that collects events into a channel.
 pub struct ChannelEventCollector {
     collision_event_sender: Sender<CollisionEvent>,
     contact_force_event_sender: Sender<ContactForceEvent>,
 }
 
 impl ChannelEventCollector {
-    /// Initialize a new collision event handler from crossbeam channel senders.
+    /// Initialize a new collision event handler from channel senders.
     pub fn new(
         collision_event_sender: Sender<CollisionEvent>,
         contact_force_event_sender: Sender<ContactForceEvent>,