WIP: Convert RuntimeStrategyFactory to std::function<>

Note that for unknown reasons, this does not yet work.
15 jobs for std-function-based-factory in 1 minute and 35 seconds (queued for 1 second)
Name Stage Failure
smoke-test Smoke Test
Fail:               3   
Unexpected Pass: 0
Skipped: 0
Timeout: 0

Full log written to /builds/flow/emper/build-debugoptimized/meson-logs/testlog.txt
make: *** [Makefile:45: smoke-test] Error 3
Cleaning up file based variables
ERROR: Job failed: exit code 1