Add judge input to custom checker

[xxori]

As defined here, custom checkers can take a kwargs object containing additional info. One particularly useful one I would like the cli to provide is the input file, as this is useful in a lot of checking scripts. Additionally, we cannot pass it through argv as we passed the other information, as it will be too large, so I use stdin piping here. We may need to switch to some other solution, as judge or process output may also be too large in some cases, but I forsee this being far more unlikely.

[Copilot]

Pull request overview

Adds support for providing the test case input to Python-based custom checkers in aucpl problem test, aligning with the concept of “additional checker info” via kwargs.

Changes:

• Pipe the test input file into the checker runner via stdin and forward it to check(...) as judge_input.
• Update the CLI’s embedded Python wrapper to read stdin and pass judge_input into the checker call.
• Update README custom checker signature documentation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
crates/cli/src/problem/test.rs	Pipes input file to checker via stdin and passes it to check as judge_input.
README.md	Updates custom-checker documentation to mention the new input parameter.

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