scripts: add yosupo.py Library Checker judge helpers

[devin-ai-integration]

Summary

New scripts/yosupo.py (uv script, stdlib + existing competitive-verifier dep via scripts/bundle.py) talks to the Library Checker REST API (https://v3.api.judge.yosupo.jp, the same API the frontend uses):

• yosupo.py status — scans verify/*.test.cpp for competitive-verifier: PROBLEM slugs (multiple files per problem supported) and cross-references /users/{name}/statistics solved_map, so you can see which problems you have code for vs. what's AC/LATEST_AC on the judge (plus problems solved online with no local verify file).
• yosupo.py status --compare — additionally fetches the sources of your recent AC submissions per problem (--depth, default 5) and compares each local bundle against them (normalized: #line directives, blank lines, trailing whitespace stripped). Exact match against any recent AC → up-to-date (matches #id); otherwise differs from #id (+N/-M lines) so you can judge whether the drift warrants resubmitting.
• yosupo.py table [--todo] — every judge problem grouped by the judge's own categories (/categories), with columns for local verify file and judge AC status; --todo filters to problems missing either.
• yosupo.py diff verify/foo.test.cpp [--submission ID] — unified diff of the local bundle vs. your latest AC (or a specific submission).
• yosupo.py submissions [--problem P] [--user U] — lists your submissions via /submissions.
• yosupo.py submit verify/foo.test.cpp [--wait] — bundles with bundle.bundle(), infers the slug from the PROBLEM comment, POSTs /submit, and with --wait polls /submissions/{id} until a terminal status (exit 0 iff AC).
• yosupo.py login — Firebase email/password sign-in; stores the refresh token at ~/.config/yosupo/credentials.json (0600) and auto-refreshes ID tokens. Reads work without login given --user; only submit needs auth.

Verified against the live judge: status [--compare], table, diff, and submissions work; submit is untested pending login credentials.

Link to Devin session: https://app.devin.ai/sessions/bec160822d544e04b8db2be3d17bdb00
Requested by: @ecnerwala

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[devin-ai-integration]

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[github-actions]

GCC Code Coverage Report

📂 Overall coverage

Metric	Coverage
Lines	🟢 6341/6920 (91.6%)
Functions	🟡 862/1024 (84.2%)
Branches	🔴 5605/7868 (71.2%)

[beta-devin-ai-integration]

Devin Review found 1 potential issue.

View 3 additional findings in Devin Review.

[beta-devin-ai-integration]

🟨 Credential file briefly world-readable before permissions are tightened

In scripts/yosupo.py:76-79, save_creds writes the Firebase refresh/ID tokens to ~/.config/yosupo/credentials.json via write_text (which creates the file using the process umask, typically 0644) and only afterwards calls chmod(0o600). Between the write and the chmod there is a brief window where the file containing long-lived auth tokens is readable by other local users.

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