Lay the groundwork for collaborating on assistant panel (#13991)

This pull request introduces collaboration for the assistant panel by
turning `Context` into a CRDT. `ContextStore` is responsible for sending
and applying operations, as well as synchronizing missed changes while
the connection was lost.

Contexts are shared on a per-project basis, and only the host can share
them for now. Shared contexts can be accessed via the `History` tab in
the assistant panel.

<img width="1819" alt="image"
src="https://github.com/zed-industries/zed/assets/482957/c7ae46d2-cde3-4b03-b74a-6e9b1555c154">


Please note that this doesn't implement following yet, which is
scheduled for a subsequent pull request.

Release Notes:

- N/A

crates/clock/Cargo.toml

@@ -18,4 +18,5 @@ test-support = ["dep:parking_lot"]
 [dependencies]
 chrono.workspace = true
 parking_lot = { workspace = true, optional = true }
+serde.workspace = true
 smallvec.workspace = true

crates/clock/src/clock.rs

@@ -1,5 +1,6 @@
 mod system_clock;
 
+use serde::{Deserialize, Serialize};
 use smallvec::SmallVec;
 use std::{
     cmp::{self, Ordering},
@@ -16,7 +17,7 @@ pub type Seq = u32;
 
 /// A [Lamport timestamp](https://en.wikipedia.org/wiki/Lamport_timestamp),
 /// used to determine the ordering of events in the editor.
-#[derive(Clone, Copy, Default, Eq, Hash, PartialEq)]
+#[derive(Clone, Copy, Default, Eq, Hash, PartialEq, Serialize, Deserialize)]
 pub struct Lamport {
     pub replica_id: ReplicaId,
     pub value: Seq,
@@ -161,6 +162,10 @@ impl Lamport {
         }
     }
 
+    pub fn as_u64(self) -> u64 {
+        ((self.value as u64) << 32) | (self.replica_id as u64)
+    }
+
     pub fn tick(&mut self) -> Self {
         let timestamp = *self;
         self.value += 1;