Fix binary stdin and stdout handling in the code-generation judge - #161

Fixes #160.

Summary

Fix binary standard I/O handling in the code-generation judge.

• Make sys.stdin.buffer use a cursor-backed byte stream, so consecutive readline() calls consume consecutive lines.
• Make text and binary stdin reads share the same input position. Remove the separate stdin method patches that could return inconsistent data.
• Capture sys.stdout.buffer.write(...) while preserving the order of text and binary writes.
• Add regression tests for binary reads and writes, mixed text/binary I/O, and the standard-I/O judging path.

Validation

• 8 new regression tests passed in the 0.5.18 Docker environments.
• Rejudged the same extracted solutions and test cases from a full 175-problem LiveCodeBench v6 run generated with SGLang 0.5.18:
  • Unmodified upstream judge: 154/175
  • This PR: 159/175
  • 5 problems changed from fail to pass; none changed from pass to fail.

The recovered problems are abc391_f (stdin.buffer.readline()) and abc393_e, abc398_f, abc398_d, and arc191_a (stdout.buffer).