Support local testing

### Describe the enhancement requested

Currently some test files are being generated by CI scripts. This means they are not accessible in a local clone of this repository, making local testing difficult.

The three generated files are very small, less than 1KB each:
testdata_bool.arrow
testdata_double.arrow
testdata_struct.arrow

Can these just be checked into the repo? Or at least document a generation step a developer can run locally.

(As mentioned in https://github.com/apache/arrow-swift/pull/77)

Start by locating the CI scripts that generate testdata_bool.arrow, testdata_double.arrow, and testdata_struct.arrow, then check how those files are used by local tests. Done means a developer with a local clone can run the tests using the checked-in files or a documented local generation step.

Written by the indexing model from the issue text.