refactor: optmgr to simpler design, one file

[vsoch]

Problem: the current optmanager is split into two files and it adds unneeded complexity. There might have been some initial intention for such a design, but it seems overkill for a small class that manages options. Solution: refactor all functions to just be in one file.

I also added the C++ extensions to be provided by the default for the DevContainer - without it I miss the "customize your environment" option that pops up and then allows me to choose my compiler, etc. to get the nice testing buttons on the side. :red_circle: :green_circle:

I chat with @trws about this in our last meeting.

[vsoch]

I'd love to! This was easy and fun. I really appreciate small tasks like this that will (slowly) get me more familiar with fluxion and C++. I'm hoping with enough exposure things will start to click at some point.

[vsoch]

Do I need to rebase and then do merge when passing?

[trws]

I actually don't see any need for a rebase, it's all up to date, and the commit messages look good. Feel free to set MWP.

[vsoch]

If I remember, my researchapps org might not work with the merge train, but we can try again. If it doesn't I can switch over to manbat or just use vsoch.

[vsoch]

woot!