Merge branch 'restructure-tests' into 'master'

tests/io/AlarmFutureTest.cpp

tests/io/CancelFutureTest.cpp

tests/io/ConcurrentNetworkEchoTest.cpp

tests/io/FutureCallbackTest.cpp

tests/io/IncrementalCompletionTest.cpp

tests/io/LinkFutureTest.cpp

tests/io/ReuseFutureTest.cpp

tests/io/SimpleDiskAndNetworkTest.cpp

tests/io/SimpleNetworkTest.cpp

tests/io/TimeoutWrapperTest.cpp

tests/io/TooLongFutureChain.cpp

tests/io/meson.build

tests/lib/MathTest.cpp

tests/lib/TemplateUtilTest.cpp

tests/lib/meson.build

tests/meson.build