Use serde 1.0.221 instead of serde_derive hackery (#38137)

serde 1.0.221 introduced serde_core into the build graph, which should
render explicitly depending on serde_derive for faster build times an
obsolote method.

Besides, I'm not even sure if that worked for us. My hunch is that at
least one of our deps would have `serde` with derive feature enabled..
and then, most of the crates using `serde_derive` explicitly were also
depending on gpui, which depended on `serde`.. thus, we wouldn't have
gained anything from explicit dep on `serde_derive`

Release Notes:

- N/A

crates/eval/src/examples/mod.rs

@@ -115,6 +115,10 @@ pub struct ExampleToml {
     pub url: String,
     pub revision: String,
     pub language_extension: Option<String>,
+    #[expect(
+        unused,
+        reason = "This field was found to be unused with serde library bump; it's left as is due to insufficient context on PO's side, but it *may* be fine to remove"
+    )]
     pub insert_id: Option<String>,
     #[serde(default = "default_true")]
     pub require_lsp: bool,