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/db/src/kvp.rs

@@ -18,8 +18,13 @@ impl KeyValueStore {
         }
     }
 
+    pub async fn write_kvp(&self, key: String, value: String) -> anyhow::Result<()> {
+        log::debug!("Writing key-value pair for key {key}");
+        self.write_kvp_inner(key, value).await
+    }
+
     query! {
-        pub async fn write_kvp(key: String, value: String) -> Result<()> {
+        async fn write_kvp_inner(key: String, value: String) -> Result<()> {
             INSERT OR REPLACE INTO kv_store(key, value) VALUES ((?), (?))
         }
     }
@@ -78,8 +83,13 @@ impl GlobalKeyValueStore {
         }
     }
 
+    pub async fn write_kvp(&self, key: String, value: String) -> anyhow::Result<()> {
+        log::debug!("Writing global key-value pair for key {key}");
+        self.write_kvp_inner(key, value).await
+    }
+
     query! {
-        pub async fn write_kvp(key: String, value: String) -> Result<()> {
+        async fn write_kvp_inner(key: String, value: String) -> Result<()> {
             INSERT OR REPLACE INTO kv_store(key, value) VALUES ((?), (?))
         }
     }