Support test_dir options

[jakubsob]

Motivation

I want to use custom testthat reporter when running rhino::test_r

Feature description

rhino::test_r allows to pass arguments to testthat::test_r

Implementation ideas

No response

Impact

Some CI workflows may require custom testthat reporter in order to correctly show test results. This could help with rhino adoption in projects with such requirements

Comments

No response