`nullptr` context in standard library

[codygunton]

Null pointers are uses as the default context (pointer to a builder). This was a frequent source of issues when building the circuit simulator because we'd to access, for example, the failed state of the composer and get a segfault. Is there any subtle logic around the use of the nullptr context when we're constructing circuit constants? I think it would be best to always initialize the context and git rid of any special nullptr logic that exists in favor of something more explicit, and something that does not conflict with the strategy I took for the simlator.

[kevaundray]

std::optional probably makes sense here, most of the logic around nullptr IIRC is just there to see if it has been set, if not then the stdlib type is likely a constant

[codygunton]

Note that the simulator has been scrapped but the questions above the issue is still worth investigating.