Add ElectrumSync builder for one-liner wallet synchronization

- Implement fluent API for Electrum sync configuration
- Add type alias to resolve clippy complexity warning
- Include comprehensive documentation and examples
- Add new bdk_builder module with sync functionality

Author: +Sharon

crates/electrum/Cargo.toml

@@ -16,7 +16,7 @@ workspace = true
 [dependencies]
 bdk_core = { path = "../core", version = "0.6.1" }
 bdk_chain = { path = "../chain" }
-electrum-client = { version = "0.24.0", features = [ "proxy" ], default-features = false }
+electrum-client = { version = "0.24.0", features = [ "proxy" ] }
 
 [dev-dependencies]
 bdk_testenv = { path = "../testenv" }

crates/electrum/src/bdk_builder.rs

@@ -146,7 +146,6 @@ where
         for (keychain_id, spk_iter) in self.wallet.all_unbounded_spk_iters() {
             builder = builder.spks_for_keychain(keychain_id, spk_iter);
         }
-
         builder.build()
     }
-}
+}