refactor: improve error message when sniper printer is set after building model

[slarse]

Fix #3693

The sniper printer must be set in the environment before building the model in order for the change collector (which is otherwise unnecessary overhead) to be attached. The error message you currently get if you set the sniper after building the model is uninformative to the uninitiated, and just says:

ChangeCollector was not attached to the environment

This PR augments that error message to say:

ChangeCollector was not attached to the environment. This typically means that the Sniper printer was set after building the model. It must be set before building the model.

I think this should be less confusing for non-expert users that run into this error (I was confused at first).

[slarse]

I'm not sure what tag (i.e. feat: doc: etc) to use in the PR title, so feel free to choose one that's appropriate!

[monperrus]

Thanks! Decided to go for a refactor: commit prefix: same behavior, but better for the developer.