fix: remove tower as dependency for wasm32-unknown-unknown

[jlizen]

Closes #2509

This addresses the change likely that caused the wasm regression.

(EDIT: I've now reproduced the failure and can confirm this fixes it)

---

Changes to dependencies on wasm32-unknown-unknown:

Old (has tower):

> cargo tree --target wasm32-unknown-unknown

reqwest v0.12.11 (/workplace/jlizen/reqwest)
<snip>
├── tower v0.5.2
│   ├── futures-core v0.3.31
│   ├── futures-util v0.3.31 (*)
│   ├── pin-project-lite v0.2.15
│   ├── sync_wrapper v1.0.2 (*)
│   ├── tokio v1.42.0
│   │   └── pin-project-lite v0.2.15
│   ├── tokio-util v0.7.13
│   │   ├── bytes v1.9.0
│   │   ├── futures-core v0.3.31
│   │   ├── futures-sink v0.3.31
│   │   ├── pin-project-lite v0.2.15
│   │   └── tokio v1.42.0 (*)
│   ├── tower-layer v0.3.3
│   ├── tower-service v0.3.3
│   └── tracing v0.1.41
│       ├── pin-project-lite v0.2.15
│       └── tracing-core v0.1.33
│           └── once_cell v1.20.2
├── tower-service v0.3.3
<snip>
[dev-dependencies]
<snip>

New (tower is only for tests):

cargo tree --target wasm32-unknown-unknown
reqwest v0.12.11 (/workplace/jlizen/reqwest)
<snip>
├── tower-service v0.3.3
<snip>
[dev-dependencies]
<snip>
├── tower v0.5.2
│   ├── futures-core v0.3.31
│   ├── pin-project-lite v0.2.15
│   ├── tokio v1.42.0
│   │   └── pin-project-lite v0.2.15
│   ├── tokio-util v0.7.13
│   │   ├── bytes v1.9.0
│   │   ├── futures-core v0.3.31
│   │   ├── futures-sink v0.3.31
│   │   ├── pin-project-lite v0.2.15
│   │   └── tokio v1.42.0 (*)
│   ├── tower-layer v0.3.3
│   ├── tower-service v0.3.3
│   └── tracing v0.1.41
│       ├── pin-project-lite v0.2.15
│       └── tracing-core v0.1.33
│           └── once_cell v1.20.2
<snip>

[jlizen]

Got a reproduction from @jonatino and confirmed that the fix is good. Will follow up with a change to improve CI separately.

[seanmonstar]

Thanks for the quick patch!