Suggest --snifflimit 0 for non-seekable input

[sapunyangkut]

Summary

• detect the exact io.UnsupportedOperation raised when dialect sniffing tries to rewind non-seekable standard input
• suggest the existing --snifflimit 0 workaround without changing other exception output
• add positive and negative regression coverage and document the change in the Unreleased changelog

Fixes #1344.

Validation

• focused CLI tests: 13 passed on the exact upstream base and patch
• full suite: 359 passed plus 31 subtests on the exact upstream base and patch
• flake8, isort, and check-manifest passed on the exact upstream base and patch
• four direct exception-handler self-tests, Python AST checks, and git diff --check passed in the publication worktree
• the current publication environment could not recollect pytest because agate is not installed; no dependencies were installed for this submission

AI assistance disclosure

This change was prepared and tested with OpenAI Codex. It is intentionally opened as a Draft for maintainer review. No automated issue/PR comments or Ready transition will be made.