Describe the Bug

While pyrefly correctly handles sys.platform guards (recognizing them as platform narrowing), it does not recognize os.name as a platform guard. This causes false positives for Windows-only attributes that are conditionally accessed behind os.name == "nt" checks.

Minimal repro:

import os
import subprocess
if os.name == "nt":
    flags = subprocess.CREATE_NO_WINDOW  # FP: No attribute `CREATE_NO_WINDOW`
else:
    flags = 0

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeSIEAtsbgE4AuABLnADrrW2NNwCu2YnVwBjeO05gWcQulRUYTALxKmbEOgbrEHJnqZgoqAOZxlvAUNHjCAYQBKAUQCCAFUcB9AHIB5DwHUASS8AER9-PQBiJgAxAAVEJi9cJlQGBjoIbD4GRQADBxd3bz8g0PC8jhgoOBgddH0DI1NzAAYQABoQHOgZMgpogFUGaAgGUgM%2BdBER3HQJDkwYKTB6KjSPdD4qbBg6AAp8RIhNAEomAFoAPl4M%2Bsa6GAY%2BOgawdS9t3bpE4HwAX3UHE6IDIj0MpEIDFwVCgAyYcVI4KgEzQWDw%2BCYIjmkGMLzSEDmhA40QAyjBFAALdLEOCIAD09LByxRhHoxnpMHQ9Mwojg9Ox6Fx%2BNm3IM9FSADdUNBUNhYFicRA8XQCXMWMRRTIOGQGJS5hdJXs4ISGqp1ABmQgARgATED0CB-l1UDMIEaYtAYBQ0TgCCRyP8gA

(Only applicable for extension issues) IDE Information

No response