Fix asio::co_composed crash on MSVC

[annihilatorq]

see: chriskohlhoff/asio#1724

this pr fixes a bug related to asio by using the alignment capability built into asio::co_composed_future with a custom allocator bound to the completion token

the union inside asio::co_composed_future will take alignof(allocator_type), and allocator_type will be the allocator associated with the completion token. therefore, all we need to do is create a simple allocator with alignas(16), after which the compiler will automatically align asio::co_composed_future::block by 16 bytes, and the SSE movaps instruction, which was incorrectly emitted by the MSVC, will be able to be executed correctly without triggering STATUS_ACCESS_VIOLATION (GP fault)

[annihilatorq]

in that case, it would be good to extend the CI matrix for MSVC (including /O2 builds)
it may also be worth cleaning up the code, as completion-token type deducing was added in asio-1.31, which allows us to get rid of the unnecessary bound_token variable before each call to async_initiate

[annihilatorq]

it may also be worth cleaning up the code, as completion-token type deducing was added in asio-1.31, which allows us to get rid of the unnecessary bound_token variable before each call to async_initiate

pr will be appreciated 😎. closed.