Change default compilation mode to dev / debug mode

[plajjan]

Change default from release to dev build. Most of the time we want to iterate while developing. Debug builds are faster to build and with debug symbols and some UB sanitization that we likely want while developing and testing.

[mzagozen]

So I learned the other day that acton test implies a development build for the current project. But this does not apply for the deps listed in build.act.json. That seems like a mistake and diverges from acton build --dev where the deps are built for development.

[plajjan]

@mzagozen ok. Yeah, I think build mode should be propagated to deps regardless if it's explicitly invoked as a build or indirectly via test. Makes sense...