chore: reduce warnings when compiling non-wasm (#1796)

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> [!IMPORTANT]
> Add conditional compilation for `aws_cred_bridge` in `lib.rs` to
reduce non-WASM compile errors.
> 
>   - **Compilation**:
> - Add `#[cfg(target_arch = "wasm32")]` to `aws_cred_bridge` module in
`lib.rs` to prevent compile errors when not targeting WebAssembly.
> 
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=BoundaryML%2Fbaml&utm_source=github&utm_medium=referral)<sup>
for bf9dbb4. It will automatically
update as commits are pushed.</sup>

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Author: sxlijin

engine/baml-schema-wasm/src/lib.rs

@@ -1,3 +1,4 @@
+#[cfg(target_arch = "wasm32")]
 pub(crate) mod aws_cred_bridge;
 
 #[cfg(target_arch = "wasm32")]