Move buffer diff storage from BufferStore to GitStore (#26795)

Release Notes:

- N/A

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: max <max@zed.dev>

crates/client/src/user.rs

@@ -29,6 +29,12 @@ impl std::fmt::Display for ChannelId {
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
 pub struct ProjectId(pub u64);
 
+impl ProjectId {
+    pub fn to_proto(&self) -> u64 {
+        self.0
+    }
+}
+
 #[derive(
     Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy, serde::Serialize, serde::Deserialize,
 )]