Add required serde_derive feature flag to bevy_ecs (#17651)

# Objective

```
cargo test --package bevy_ecs --lib --all-features
```

fails to compile, with output like

> error[E0433]: failed to resolve: could not find `Serialize` in `serde`
>    --> crates/bevy_ecs/src/entity/index_set.rs:14:69
>     |
> 14 | #[cfg_attr(feature = "serialize", derive(serde::Deserialize,
serde::Serialize))]
> | ^^^^^^^^^ could not find `Serialize` in `serde`
>     |
> note: found an item that was configured out
> -->
/home/alice/.cargo/registry/src/index.crates.io-6f17d22bba15001f/serde-1.0.217/src/lib.rs:343:37
>     |
> 343 | pub use serde_derive::{Deserialize, Serialize};
>     |                                     ^^^^^^^^^
> note: the item is gated behind the `serde_derive` feature
> -->
/home/alice/.cargo/registry/src/index.crates.io-6f17d22bba15001f/serde-1.0.217/src/lib.rs:341:7
>     |
> 341 | #[cfg(feature = "serde_derive")]
>     |       ^^^^^^^^^^^^^^^^^^^^^^^^


## Solution

Add the required feature flags and get bevy_ecs compiling standalone
corrctly.

## Testing

The command above now compiles succesfully. Note that several system
stepping tests are failing, and were not being tested in CI. That's a
different PR's problem though.

crates/bevy_ecs/Cargo.toml

@@ -119,6 +119,7 @@ disqualified = { version = "1.0", default-features = false }
 fixedbitset = { version = "0.5", default-features = false }
 serde = { version = "1", default-features = false, features = [
   "alloc",
+  "serde_derive",
 ], optional = true }
 thiserror = { version = "2", default-features = false }
 derive_more = { version = "1", default-features = false, features = [