fix(tests): skip POSIX-only and symlink tests on Windows CI

Five tests were silently failing on the Windows CI job because they
either required a Linux/macOS runtime or created symlinks (which the
default Windows user cannot do without Developer Mode).

Mark them with the project's existing linux_only / require_symlinks
markers so CI on Windows skips them cleanly instead of reporting red:

* TestPosixNoOp, test_noop_on_posix, test_no_hermes_home_returns_native
  -> @pytest.mark.linux_only (the asserts only make sense on POSIX
  where '~/.hermes' is the natural HERMES_HOME fallback).
* test_atomic_replace_copy_fallback_preserves_symlink,
  test_symlinked_target_survives_a_contended_rename
  -> @pytest.mark.require_symlinks (matches the pattern already used
  by sibling tests in the same file).

For the two symlink tests in test_hermes_constants.py that weren't
covered by require_symlinks, wrap the symlink_to() call in a
try/except(OSError, NotImplementedError) -> pytest.skip() so a host
without symlink privilege still skips instead of erroring out.

No production code touched. Verified locally on win32 Python 3.11.9:
88 passed, 25 skipped, 0 failed across the three files (down from
7 failed, 88 passed).

tests/test_atomic_replace_symlinks.py

@@ -224,6 +224,7 @@ def test_atomic_replace_broken_symlink_creates_target(tmp_path: Path) -> None:
 
 
 
+@pytest.mark.require_symlinks
 def test_atomic_replace_copy_fallback_preserves_symlink(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch
 ) -> None:
@@ -506,6 +507,7 @@ def test_in_place_rewrite_never_exposes_a_truncated_file(
     assert observed == [5000]
 
 
+@pytest.mark.require_symlinks
 def test_symlinked_target_survives_a_contended_rename(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch, fast_replace_retries: None
 ) -> None:

tests/test_hermes_bootstrap.py

@@ -120,6 +120,7 @@ class TestUserOptOut:
 
 
 
+@pytest.mark.linux_only
 class TestPosixNoOp:
     """POSIX: zero behavior change.  We don't touch LANG, LC_*, or any
     stdio.  The goal is that Linux/macOS behave identically before and
@@ -336,6 +337,7 @@ class TestHardenImportPath:
 class TestSuppressPlatformVerConsole:
     """suppress_platform_ver_console: stub applied on Windows, no-op on POSIX."""
 
+    @pytest.mark.linux_only
     def test_noop_on_posix(self):
         import platform
         hb = _fresh_import()

tests/test_hermes_constants.py

@@ -33,6 +33,7 @@ from hermes_constants import (
 class TestGetDefaultHermesRoot:
     """Tests for get_default_hermes_root() — Docker/custom deployment awareness."""
 
+    @pytest.mark.linux_only
     def test_no_hermes_home_returns_native(self, tmp_path, monkeypatch):
         """When HERMES_HOME is not set, returns ~/.hermes."""
         monkeypatch.delenv("HERMES_HOME", raising=False)
@@ -759,7 +760,10 @@ class TestGetHermesDir:
         """
         self._set_home(tmp_path, monkeypatch)
         legacy = tmp_path / "pairing"
-        legacy.symlink_to(tmp_path / "does-not-exist")
+        try:
+            legacy.symlink_to(tmp_path / "does-not-exist")
+        except (OSError, NotImplementedError) as exc:
+            pytest.skip(f"Symlink not supported on this platform/permission: {exc}")
         new = tmp_path / "platforms" / "pairing"
         new.mkdir(parents=True)
         (new / "discord-approved.json").write_text("[]")
@@ -773,7 +777,10 @@ class TestGetHermesDir:
         real.mkdir()
         (real / "cached.png").write_bytes(b"x")
         legacy = tmp_path / "image_cache"
-        legacy.symlink_to(real)
+        try:
+            legacy.symlink_to(real)
+        except (OSError, NotImplementedError) as exc:
+            pytest.skip(f"Symlink not supported on this platform/permission: {exc}")
         result = get_hermes_dir("cache/images", "image_cache")
         assert result == legacy