fix: block remote CSV redirects

[LuisFigueroaG]

Summary

• fetch remote CSV URLs with an opener that rejects HTTP redirects instead of following them implicitly
• surface redirect responses as RemoteReadError with the original URL and HTTP status
• add a local HTTP 302 regression test for remote CSV fetches

Closes #2614

Validation

• uv run pytest -q tests/test_remote_csv.py
• uv run ruff format --check arnio/io.py tests/test_remote_csv.py
• uv run ruff check arnio/io.py tests/test_remote_csv.py
• uv run ruff check .
• uv run pytest -q
• git diff --check

Known existing environment/project issues:

• uv run ruff format --check . reports pre-existing formatting changes in 33 unrelated files
• uv run pyright fails because the pyright executable is not installed in the uv environment

[vercel]

@LuisFigueroaG is attempting to deploy a commit to the xtylishanish-gmailcom's projects Team on Vercel.

A member of the Team first needs to authorize it.