Tests: Move data within testthat calls

[bms63]

Background

Please see #2978 for additional background and discussion.

The tests in "tests/testthat/test-derive_param_bsa.R" have data being created outside of the testthat calls which can have unintended side effects.

The data should be moved inside the testthat calls if it is small. For data that is large or repeatedly used throughout tests another method should be used, e.g. use of withr and/or creating an additional subfolder within testthat called testdata. All efforts should be made to ensure data does not spillover into another test.

Definition of done

• Tests in "tests/testthat/test-derive_param_bsa.R" have all data self-contained
• Test Data is documented as needed

[bms63]

@adcascone do you have the Assign Copilot?