[ArrowStringArray] TST: parametrize str.split tests
the test (and benchmark) changes broken off from #41085 as a precursor to #41085 and #41372 (which currently makes changes to the str.split path, although I may break that PR up also)
these are the current timings for master (will hopefully get improvements for object fallback by breaking off changes in  #41372 and also by using pyarrow kernels #41085)

```
 25.00%] ··· strings.Split.time_rsplit                                                                                                                   ok
[ 25.00%] ··· ============== ========== ==========
              --                     expand       
              -------------- ---------------------
                  dtype         True      False   
              ============== ========== ==========
                   str        82.2±0ms   33.5±0ms 
                  string      66.9±0ms   29.9±0ms 
               arrow_string   88.0±0ms   33.7±0ms 
              ============== ========== ==========

[ 50.00%] ··· strings.Split.time_split                                                                                                                    ok
[ 50.00%] ··· ============== ========== ==========
              --                     expand       
              -------------- ---------------------
                  dtype         True      False   
              ============== ========== ==========
                   str        107±0ms    56.8±0ms 
                  string      92.4±0ms   54.3±0ms 
               arrow_string   111±0ms    58.0±0ms 
              ============== ========== ==========
``` Thanks Simon!