Public API for advancing the CVM timestamp

[helins]

I've been using a hacky way for advancing the CVM timestamp (and executing scheduled transactions) that broke recently. Important for testing scheduling deterministically.

Note: not a priority for cloud testing per se but avoids breaking the current tooling (i.e. Shell)

[mikera]

A couple of potentially useful functions have been made public in State so you should be able to do this.

Note however this is internal stuff and not likely to be part of any official public API, so caveat emptor as usual.....

[mikera]

Please confirm if the above solves your problem and close if so, thanks @helins

[helins]

Does the job, thanks. I would keep it more official since it is the only way of reliably testing scheduling (which is a key feature of Convex).