Inefficient executeHashComputations of hashtree

[twoeths]

benchmark does not show great executeHashComputations() performance on Linux, for example in https://github.com/ChainSafe/ssz/actions/runs/14090676972/job/39466309168

hashtree
    ✔ getHashComputations                                                 369.1343 ops/s    2.709041 ms/op   x1.226        119 runs   12.2 s
    ✔ executeHashComputations                                             100.3185 ops/s    9.968249 ms/op   x0.[90](https://github.com/ChainSafe/ssz/actions/runs/14090676972/job/39466309168#step:6:91)5         50 runs   4.91 s
    ✔ get root                                                            65.38101 ops/s    15.29496 ms/op   x1.030         12 runs   2.27 s

executeHashComputations is only 50% faster than get root, on our typical Linux node it's only 30% faster

however on my Macbook, it's 150% faster.