[BUG] http feature is not additive

### Is there an existing issue for this?

- [X] I have searched the existing issues

### What version of `workers-rs` are you using?

0.0.21

### What version of `wrangler` are you using?

3.37.0

### Describe the bug

The `http` feature is not additive, which is necessary for [feature unification](https://doc.rust-lang.org/cargo/reference/features.html#feature-unification) to work. This prevents, e.g. multiple workers in the same workspace from using different feature sets.

### Steps To Reproduce

1. Create a Cargo workspace with two workers
2. In one worker, use the `http` feature
3. In another worker, do not use the `http` feature.
4. Observe that the non-http worker cannot compile.