Ensure that most / all async methods in the SDK return futures that are `Send` (except on WASM)

Currently, we have `#[cfg_attr(not(target_arch = "wasm32"), deny(clippy::future_not_send))]` in a few select places. We should apply it more broadly and fix all of the issues it finds.

Locate the existing #[cfg_attr(not(target_arch = "wasm32"), deny(clippy::future_not_send))] uses and inspect the async SDK methods covered by those modules. Run Clippy with future_not_send enabled on non-WASM targets, then address the reported methods and verify that the lint passes while WASM remains exempt.

Written by the indexing model from the issue text.