functions to get the (flattened) list of results by type

[nickrobinson251]

e.g. like https://github.com/JuliaTesting/ReTestItems.jl/blob/498097bd04a9f890b8623c0d0857ab5dd534890d/test/_integration_test_tools.jl#L71-L89

effectively a generalisation of the current nonpassing_results

[nickrobinson251]

i'm thinking the usage would be like:

@testset begin
    results = capture_results() do  # <- return an EncasedTestSet, so we can iterrogate the results
       my_tester_function() 
    end
    # test we saw the one error we expected
    err = only(get_errors(results))
    @test err.test_type == :nontest_error
    @test err.value == string(ErrorException("test item \"Abort\" didn't succeed after 1 tries"))
end