tests: add 'f' tool for cross platform file operations in the tests This tool is like the collection of tools found in a unix environment but are cross platform and stable and suitable for our needs in the test suite. The main reason it is "needed" now is for hexdump of revision branch cache to keep an eye on how it changes and make sure the format is stable. It is a very generic tool that can end up being used a lot in tests, so I gave it very generic name.