clock: Cleanup ReplicaId, Lamport and Global (#40600)

- Notable change is the use of a newtype for `ReplicaId`
- Fixes `WorktreeStore::create_remote_worktree` creating a remote
worktree with the local replica id, though this is not currently used
- Fixes observing the `Agent` (that is following the agent) causing
global clocks to allocate 65535 elements
- Shrinks the size of `Global` a bit. In a local or non-collab remote
session it won't ever allocate still.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/client/src/user.rs

@@ -943,7 +943,7 @@ impl Collaborator {
     pub fn from_proto(message: proto::Collaborator) -> Result<Self> {
         Ok(Self {
             peer_id: message.peer_id.context("invalid peer id")?,
-            replica_id: message.replica_id as ReplicaId,
+            replica_id: ReplicaId::new(message.replica_id as u16),
             user_id: message.user_id as UserId,
             is_host: message.is_host,
             committer_name: message.committer_name,