cli.output: use subprocess.DEVNULL in PlayerOutput

Instead of passing `os.devnull` file-handles to `subprocess.Popen`,
use the `subprocess.DEVNULL` identifier for stdout/stderr streams.

This avoids `ResourceWarning`s in tests when the file-handles don't get
closed despite never calling `PlayerOutput.open()`, as they were already
opened in the `PlayerOutput`'s constructor, e.g. during test collection
in parametrized tests without indirect fixtures.

Also call `PlayerOutput.close()` in tests where a *mocked* player output
was explicitly opened.

src/streamlink_cli/output.py

@@ -117,8 +117,8 @@ class PlayerOutput(Output):
             self.stdin = subprocess.PIPE
 
         if self.quiet:
-            self.stdout = open(os.devnull, "w")
-            self.stderr = open(os.devnull, "w")
+            self.stdout = subprocess.DEVNULL
+            self.stderr = subprocess.DEVNULL
         else:
             self.stdout = sys.stdout
             self.stderr = sys.stderr
@@ -203,18 +203,12 @@ class PlayerOutput(Output):
         return shlex.split(cmd) + extra_args + shlex.split(args)
 
     def _open(self):
-        try:
-            if self.record:
-                self.record.open()
-            if self.call and self.filename:
-                self._open_call()
-            else:
-                self._open_subprocess()
-        finally:
-            if self.quiet:
-                # Output streams no longer needed in parent process
-                self.stdout.close()
-                self.stderr.close()
+        if self.record:
+            self.record.open()
+        if self.call and self.filename:
+            self._open_call()
+        else:
+            self._open_subprocess()
 
     def _open_call(self):
         args = self._create_arguments()

tests/cli/output/test_playeroutput.py

@@ -1,4 +1,3 @@
-from contextlib import suppress
 from unittest.mock import Mock, call, patch
 
 import pytest
@@ -8,11 +7,10 @@ from streamlink_cli.output import PlayerOutput
 
 @pytest.fixture()
 def playeroutput(request: pytest.FixtureRequest):
-    playeroutput = PlayerOutput(**getattr(request, "param", {}))
-    yield playeroutput
-    for stream in playeroutput.stdout, playeroutput.stderr:
-        with suppress(OSError):
-            stream.close()
+    with patch("streamlink_cli.output.sleep"):
+        playeroutput = PlayerOutput(**getattr(request, "param", {}))
+        yield playeroutput
+        playeroutput.close()
 
 
 @pytest.fixture()

tests/cli/test_streamrunner.py

@@ -175,6 +175,7 @@ class TestPlayerOutput:
             output = FakePlayerOutput("mocked")
             output.open()
             yield output
+            output.close()
 
     @pytest.fixture()
     def stream_runner(self, stream: FakeStream, output: FakePlayerOutput):