*: strip Imath versioning

and mark py-opentimelineio as USES=python:3.11+ because versions
3.10 and older fail to package (some modules do not build).

Please everyone do test your ports with

BUILD_ALL_PYTHON_FLAVORS=       yes

in your /usr/local/etc/poudriere.d/make.conf - and

poudriere bulk -Ct -j "$JAIL" multimedia/py-opentimelineio@all

(the @All is the crucial part here)