Refactor Blocking I/O in MtlsUtils

There is a the [Boq violation](http://go/boq-conformance-violations/BLOCKING) for [MtlsUtils](https://fusion2.corp.google.com/invocations/2ae0743e-d7e5-4389-a9fd-115ef50581e1/targets/%2F%2Fjavatests%2Fcom%2Fgoogle%2Fads%2Flift%2Fmmm%2Fconsultation%2Fboq:inspection_conformance_test;config=bdb61ef478e1953f27d29ce05bb3368addacc7edd8000dbc9918370a2ae221ee/tests;row=19) regarding blocking I/O when we try to migrate this repo to google3.
Even though it is not required to not having blocking I/O on Github and the code looks reasonable, we also try to avoid process spawning and blocking I/O.
Per @TimurSadykov, this code path also has a narrow use case so it may not be worth it to refactor it. Assigning to @TimurSadykov for further triaging and prioritizing.