Testing framework: add option to remove default printing

type:added

For LIGO developers

By default, the testing framework prints that all in top-level was executed, and the result of the values prefixed with test.

This MR introduces functions that allow disabling the printing of test values (so users can have more control over what to print or not).

Changelog details:

Testing framework: allow disabling of default printing.

By default, LIGO's testing framework will print the values prefixed with test. Now it is possible to disable this output by using Test.unset_print_values : unit -> unit. It can be turned on again using Test.set_print_values : unit -> unit. The values prefixed with test will be printed or not at the end of execution, depending on which of these commands was executed last.