async evolutions

The current async implementation using _start/_cont API requires applications to manually handle I/O waiting using platform-specific code (epoll/poll/select). This creates unnecessary complexity and code duplication across applications. Benchmark results show that the async API exceed synchronous performance but only when properly optimized.

Current Problems

Runtime Mode Switching is Unnecessary

MYSQL_OPT_NONBLOCK can be set/changed at any time. In practice, applications never switch between sync/async modes at runtime
This flexibility prevents optimization opportunities
Proposed: Make async mode a connection-time decision only, enabling better optimizations (optimization will even be good for standard sync version)

SSL/TLS SChannel Not Implemented

this is handled by CONC-806