Test for removed records, switch to R CMD CHECK workflow for tests, use default testthat setup

[PietrH]

• Add function to get the new, current, local to the repo, version of occurrence.csv
• Add function to get the reference, published, on github, version of occurrence.csv
• test get_current
• test get_reference
• get coverage on new helpers
• Adapt tests to use new helper functions
• Change test setup to use default testthat dirs
• Use R CMD CHECK Github action to run tests instead of running single script, so package context (exported data and functions) can be used in tests
• Move occurrence.csv to inst/data/processed/occurrence.csv instead of package root data folder, THIS REQUIRES A CHANGE ON THE IPT

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• Adapt IPT dataset

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• pass r cmd check
• pass tests
• pass lintr