Cleanup Ice/hold test

[bernardnormier]

The Ice/hold test defines an operation putOnHold:

void putOnHold(int seconds);

Despite the parameter name, the unit is actually milliseconds (I checked C++ and C#).

It would also be helpful to add comments to the operations and the tests themselves. putOnHold does not mean "put the adapter on hold for some time". When the parameter is positive, it means schedule a hold+activate in N milliseconds.

See also #766 (currently not done on the main branch).