discuss stopping criterion

[tlienart]

Proper stopping criterion (with theoretical guarantees) is when the clock in BPS or LBPS goes over a pre-specified (large) time T such as 1e8.

At the moment we're also stopping

• when the number of events generated hits a pre-specified number (in LBPS)
• when the number of gradient evaluation hits a pre-specified number (in BPS)

Both potentially add bias of some form and even though they make sense and the possibility should probably stay there, the user should be warned that the suggested choice is a maximum time.

[tlienart]

this consequently has to be sorted in src/local/simulate and src/simulate