Avoid unnecessary DB writes (#29417)

Part of https://github.com/zed-industries/zed/issues/16472

* Adds debug logging to everywhere near INSERT/UPDATEs in the DB

So something like 
`env RUST_LOG=debug,wasmtime_cranelift=off,cranelift_codegen=off,vte=off
cargo run` could be used to view these (current zlog seems to process
the exclusions odd, so not sure this is the optimal RUST_LOG line) can
be used to debug any further writes.

* Removes excessive window stack serialization

Previously, it serialized unconditionally every 100ms.
Now, only if the stack had changed, which is now check every 500ms.

* Removes excessive terminal serialization

Previously, it serialized its `cwd` on every `ItemEvent::UpdateTab`
which was caused by e.g. any character output.
Now, only if the `cwd` has changed at the next event processing time.

Release Notes:

- Fixed more excessive DB writes

crates/editor/src/items.rs

@@ -1251,6 +1251,7 @@ impl SerializableItem for Editor {
                     language,
                     mtime,
                 };
+                log::debug!("Serializing editor {item_id:?} in workspace {workspace_id:?}");
                 DB.save_serialized_editor(item_id, workspace_id, editor)
                     .await
                     .context("failed to save serialized editor")

crates/editor/src/persistence.rs

@@ -276,6 +276,7 @@ impl EditorDb {
         workspace_id: WorkspaceId,
         selections: Vec<(usize, usize)>,
     ) -> Result<()> {
+        log::debug!("Saving selections for editor {editor_id} in workspace {workspace_id:?}");
         let mut first_selection;
         let mut last_selection = 0_usize;
         for (count, placeholders) in std::iter::once("(?1, ?2, ?, ?)")
@@ -327,6 +328,7 @@ VALUES {placeholders};
         workspace_id: WorkspaceId,
         folds: Vec<(usize, usize)>,
     ) -> Result<()> {
+        log::debug!("Saving folds for editor {editor_id} in workspace {workspace_id:?}");
         let mut first_fold;
         let mut last_fold = 0_usize;
         for (count, placeholders) in std::iter::once("(?1, ?2, ?, ?)")

crates/editor/src/scroll.rs

@@ -270,6 +270,9 @@ impl ScrollManager {
 
             cx.foreground_executor()
                 .spawn(async move {
+                    log::debug!(
+                        "Saving scroll position for item {item_id:?} in workspace {workspace_id:?}"
+                    );
                     DB.save_scroll_position(
                         item_id,
                         workspace_id,