Various madmatrix improvements and bugfixes

[theoheimel]

GPU:

• reduce number of cudaMallocAsync calls in UMAMI interface
• allow for fully asynchronous calls of sigmaKin without device or stream synchronization
• allow for parallelization over helicities in a single kernel launch instead of using CUDA streams

SIMD:

• use one flavor index per SIMD vector instead of per batch
• reorder events in UMAMI such that the flavor index is the same for each vector