Merge bitcoindevkit/bdk#831: Don't default to use async/await on wasm32

32912eaa05 Don't default to use `async`/`await` on `wasm32` (Elias Rohrer)

Pull request description:

  ### Description

  We don't automatically want to make the interface `async` based on the used architecture, but now require the user to explicitly set the `async-interface` feature.

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  notmandatory:
    ACK 32912eaa05

Tree-SHA512: 41a8f3ab29508a359a8c0d96994e4fa97e52c15e8b8003c1988bcfe036cafa81d6210d446ed825672ce52aff684ebb328dc61b8ae3d25cda6f51a3cae838de58

src/blockchain/mod.rs

@@ -249,11 +249,8 @@ pub trait BlockchainFactory {
     /// operations to build a blockchain for a given wallet, so if a wallet needs to be synced
     /// often it's recommended to use [`BlockchainFactory::build_for_wallet`] to reuse the same
     /// blockchain multiple times.
-    #[cfg(not(any(target_arch = "wasm32", feature = "async-interface")))]
-    #[cfg_attr(
-        docsrs,
-        doc(cfg(not(any(target_arch = "wasm32", feature = "async-interface"))))
-    )]
+    #[cfg(not(feature = "async-interface"))]
+    #[cfg_attr(docsrs, doc(cfg(not(feature = "async-interface"))))]
     fn sync_wallet<D: BatchDatabase>(
         &self,
         wallet: &Wallet<D>,

src/lib.rs

@@ -227,7 +227,7 @@ compile_error!(
 #[cfg(feature = "keys-bip39")]
 extern crate bip39;
 
-#[cfg(any(target_arch = "wasm32", feature = "async-interface"))]
+#[cfg(feature = "async-interface")]
 #[macro_use]
 extern crate async_trait;
 #[macro_use]