Improves latency for big inlay hints LSP responses for ~8k line files.

Before, the CPU usage sample for editing a single line inside
`edirot.rs` file in Zed contained serde inside the main thread traces:

<img width="1728" alt="Screenshot 2023-06-21 at 00 33 23"
src="https://github.com/zed-industries/zed/assets/2690773/d9789efe-8055-487f-bbe7-8beb49605bcb">

Release Notes:

- N/A