Explicitly convert float to int for startTimer

[stanislavlevin]

As of Python3.10:

Builtin and extension functions that take integer arguments no longer accept Decimals, Fractions and other objects that can be converted to integers only with a loss (e.g. that have the int() method but do not have the index() method). (Contributed by Serhiy Storchaka in bpo-37999.)

startTimer accepts only integers (milliseconds) and fails to implicitly convert floats.

Fixes: https://github.com/harvimt/quamash/issues/128