async_base::complete dispatches handler without using the operation's associated executor

[ashtum]

Currently, async_base::complete passes the handler to dispatch, which may not have an associated executor. However, the operation itself (async_base) is tied to the stream's default executor. This can lead to the handler being executed on an unexpected or incorrect execution context:

beast/include/boost/beast/core/async_base.hpp

Lines 421 to 425 in 63f3d3f

	auto const ex = this->get_immediate_executor();
	net::dispatch(
	ex,
	net::append(std::move(h_), std::forward<Args>(args)...));
	wg1_.reset();