Replace lazy_static with once_cell

[nindalf]

lazy_static is used throughout the cookbook to store data that should be initialised only once. once_cell is more flexible and convenient than lazy_static. For example, it can be used for local variables.

Integrating once_cell into the standard library is in progress - issue.

I propose that the cookbook change to using once_cell instead. Once it has been integrated into the standard library, the imports alone can be changed. Until then the cookbook could reflect best practice, which is to use once_cell.