Cleanup of the Sample section

[evouga]

I've done a pass on this section. The requirements here are quite complex so please double-check everything carefully.

In particular:

• I've encouraged use of attachments where appropriate (per https://github.com/Kattis/problem-package-format/issues/338).
• Is it true that all submissions are run on the test cases in data/sample? Including in scoring problems (despite these test cases not being included in the score) and interactive problems?
• I've softened the hard requirement that interactive problems must have sample/statement and sample/download.
• Clarified that if both .interaction and .in and .out is provided, only the former is shown (is this true)?
• A strict reading of the spec suggested that interactive problems could only have a single test case in sample/statement. I assume that was unintentional?
• Clarified that downloads do not include the .interaction files by default (is this true?)
• Clarified what is means to validate the .ans files.
• Clarified that validator_args in data/sample also apply to data/sample/statement (is this true?)

[niemela]

This is a really good cleanup. Some fairly minor comments above.

[evouga]

One use case that we discussed, which is not currently well-supported, are problems where we want to display truncated or too-small sample inputs in the problem statement which (intentionally) do not pass validation.

Do we still care about this case?

If so, then in sample/statement maybe we want to allow:

• .in (required, input-validated, available for download by default), the actual input for the test case
• .displayed_in (optional, not input-validated), the input shown in the problem statement
• .ans (required), the answer_file passed to output validation
• .displayed_ans (optional, available for download by default), what is shown in the problem statement and passed to the output validator as team_output (currently called .out)

EDIT: although, this still doesn't really allow for too-small inputs...

[mzuenni]

@mzuenni, wdyt? Does this address https://github.com/Kattis/problem-package-format/issues/338? In particular, is/was your only concern the testing tool itself, and are you happy/OK with the data/sample/{.,statement,download} structure?

looks good, the structure is fine :)