Fix os.lstat for symlink paths ending with a separator (Posix)

[ghost]

Describe the changes

Under Posix, a trailing separator makes the last path component resolve, so os.lstat("link_to_dir/") returns the stat result of the directory, not of the link. The fake filesystem returns the symlink's own stat result instead. Reproduction against the real filesystem on Linux (macOS behaves the same):

import os, stat, tempfile
from pyfakefs.fake_filesystem_unittest import Patcher

def check():
    os.mkdir("dir")
    os.symlink("dir", "link")
    return stat.filemode(os.lstat("link/").st_mode)[0], os.path.islink("link/")

os.chdir(tempfile.mkdtemp())
print(check())          # ('d', False)  -- real filesystem
with Patcher():
    os.chdir("/")
    print(check())      # ('l', False)  -- pyfakefs 6.3.dev0

So the fake is also inconsistent with itself: os.path.islink("link/") already says False, while os.lstat("link/") reports a symlink. os.stat("link/", follow_symlinks=False) has the same behaviour, as it shares the code path.

FakeFilesystem.stat() already applies the trailing-separator rule when deciding whether to raise (raise_for_filepath_ending_with_separator follows the link before checking for ENOTDIR), but then returns the link's stat result. The fix resolves the link in that case and returns the directory's stat result, for Posix only; the Windows emulation is unchanged, where test_islink_with_trailing_sep_windows expects the link to be kept.

test_lstat_symlink_to_dir_with_trailing_sep_posix in fake_os_test.py fails on main and passes with the change; the RealOsModuleTest variant passes against the real filesystem (TEST_REAL_FS=1), which is where the expected values come from. The existing test_lstat_symlink_with_trailing_sep_linux/macos tests only check that lstat does not raise (#366) and still pass. Full test suite, ruff and mypy (pre-commit versions) are clean.

Found by comparing the fake filesystem with the real one on this machine over generated operation sequences.

Tasks

• Unit tests added that reproduce the issue or prove feature is working
• Fix or feature added
• Entry to release notes added
• Pre-commit CI shows no errors
• Unit tests passing (locally, fake and TEST_REAL_FS=1)
• For documentation changes: The Read the Docs preview builds and looks as expected (no documentation change)

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