Remove asio-dependent unit tests

Remove test files that require Boost.Asio:
- asio_io_context.cpp
- body_read_stream.cpp
- body_write_stream.cpp
- client.cpp
- read.cpp
- write.cpp
- wrap_executor.cpp
- sandbox.cpp
- test_helpers.hpp
- server/call_mf.cpp (missing header)
- server/route_handler_asio.cpp
- server/router_asio.cpp

Remaining 8 test suites pass with 525 assertions.

Author: vinniefalco