Add Multiplexing into cyPAPI

[Treece-Burgess]

After the December 19, 2025 lunch talk that introduced cyPAPI a user had asked if cyPAPI supported multiplexing. As stands multiplexing is not supported in cyPAPI and would need to be added.

Functionality that would need to be added into cyPAPI is:

PAPI_multiplex_init() -> cyPAPI_multiplex_init()
PAPI_set_multiplex(int EventSet) -> cyPAPI_set_multiplex(CypapiCreateEventSet)
PAPI_get_multiplex(int EventSet) -> cyPAPI_get_multiplex(CypapiCreateEventSet)