## Problem
Kattis and USACO had zero offline test coverage — no fixtures, no
conftest
routers, and no entries in the test matrix. The `precision` field and
error
paths were also unverified across all platforms.
## Solution
Add HTML fixtures for both platforms and wire up `httpx.AsyncClient.get`
routers in `conftest.py` following the existing CSES/CodeChef pattern.
Extend the test matrix from 12 to 23 parametrized cases. Add a dedicated
test for the Kattis contest-vs-slug fallback path (verifying
`contest_url`
and `standings_url`), three parametrized metadata error cases, and a
targeted assertion that `extract_precision` returns a non-`None` float
for
problems with floating-point tolerance hints.
Closes#281.
## Problem
`codeforces.py` used `curl_cffi` to bypass Cloudflare when fetching
contest problem HTML, making it unavailable in the nix python env and
requiring an extra dependency across `pyproject.toml` and `flake.nix`.
## Solution
Rewrite `_fetch_problems_html` to use scrapling `StealthySession` with
`solve_cloudflare=True`, matching the existing CF submit pattern. Extend
`needs_browser` in `scraper.lua` to route CF `metadata` and `tests`
through the FHS env on NixOS. Remove `curl-cffi` from `pyproject.toml`,
`flake.nix`, and test mocks.
