Chore: State the test directory layout in one place (#14171)

The temp directory layout used by the tests was written out four separate
times: once in the documents conftest, once in the paperless checks tests,
once in a fixture local to the NFC upload tests, and once in the helper
behind the old paperless_environment context manager. Each copy covered a
different subset of the settings, so which directories a test actually got
depended on which copy it happened to reach.

The layout now lives in paperless_testing.dirs. build_paperless_dirs owns
where things go and creates them, dirs_settings maps them onto Django
setting names and is pure, and a paperless_dirs fixture in the root conftest
applies that mapping through pytest-django's settings fixture so every app
can reach it. Tests that need a second environment part way through a test
body use the paperless_environment context manager from the same module,
which expresses the identical layout through override_settings. The three
redundant implementations and the old media settings fixture are gone, and
their consumers now take paperless_dirs.

src/paperless_testing/dirs.py

@@ -0,0 +1,131 @@
+"""The Paperless-ngx temp directory layout, stated once.
+
+``build_paperless_dirs`` owns where things go and creates them.
+``dirs_settings`` owns the mapping onto Django setting names and is pure.
+Everything else in the test suite is a caller of these two.
+"""
+
+from __future__ import annotations
+
+from contextlib import contextmanager
+from dataclasses import dataclass
+from pathlib import Path
+from tempfile import TemporaryDirectory
+from typing import TYPE_CHECKING
+from typing import TypedDict
+
+from django.test import override_settings
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
+
+
+@dataclass(frozen=True, slots=True)
+class PaperlessDirs:
+    """Standard Paperless-ngx directory layout for tests."""
+
+    data_dir: Path
+    scratch_dir: Path
+    media_dir: Path
+    consumption_dir: Path
+    static_dir: Path
+    index_dir: Path
+    originals_dir: Path
+    thumbnail_dir: Path
+    archive_dir: Path
+    logging_dir: Path
+    model_file: Path
+    media_lock: Path
+
+
+class DirSettings(TypedDict):
+    """The Django settings the layout above maps onto."""
+
+    DATA_DIR: Path
+    SCRATCH_DIR: Path
+    MEDIA_ROOT: Path
+    ORIGINALS_DIR: Path
+    THUMBNAIL_DIR: Path
+    ARCHIVE_DIR: Path
+    CONSUMPTION_DIR: Path
+    LOGGING_DIR: Path
+    INDEX_DIR: Path
+    STATIC_ROOT: Path
+    MODEL_FILE: Path
+    MEDIA_LOCK: Path
+
+
+def build_paperless_dirs(root: Path) -> PaperlessDirs:
+    """Compute the layout under root and create the directories."""
+    data_dir = root / "data"
+    media_dir = root / "media"
+    documents_dir = media_dir / "documents"
+
+    dirs = PaperlessDirs(
+        data_dir=data_dir,
+        scratch_dir=root / "scratch",
+        media_dir=media_dir,
+        consumption_dir=root / "consume",
+        static_dir=root / "static",
+        index_dir=data_dir / "index",
+        originals_dir=documents_dir / "originals",
+        thumbnail_dir=documents_dir / "thumbnails",
+        archive_dir=documents_dir / "archive",
+        logging_dir=data_dir / "log",
+        model_file=data_dir / "classification_model.pickle",
+        media_lock=media_dir / "media.lock",
+    )
+
+    for directory in (
+        dirs.data_dir,
+        dirs.scratch_dir,
+        dirs.media_dir,
+        dirs.consumption_dir,
+        dirs.static_dir,
+        dirs.index_dir,
+        dirs.originals_dir,
+        dirs.thumbnail_dir,
+        dirs.archive_dir,
+        dirs.logging_dir,
+    ):
+        directory.mkdir(parents=True, exist_ok=True)
+
+    return dirs
+
+
+def dirs_settings(dirs: PaperlessDirs) -> DirSettings:
+    """Map the layout onto Django setting names."""
+    return DirSettings(
+        DATA_DIR=dirs.data_dir,
+        SCRATCH_DIR=dirs.scratch_dir,
+        MEDIA_ROOT=dirs.media_dir,
+        ORIGINALS_DIR=dirs.originals_dir,
+        THUMBNAIL_DIR=dirs.thumbnail_dir,
+        ARCHIVE_DIR=dirs.archive_dir,
+        CONSUMPTION_DIR=dirs.consumption_dir,
+        LOGGING_DIR=dirs.logging_dir,
+        INDEX_DIR=dirs.index_dir,
+        STATIC_ROOT=dirs.static_dir,
+        MODEL_FILE=dirs.model_file,
+        MEDIA_LOCK=dirs.media_lock,
+    )
+
+
+@contextmanager
+def paperless_environment() -> Iterator[PaperlessDirs]:
+    """A second, isolated environment for the duration of the block.
+
+    Only for tests needing a fresh environment part way through a test body,
+    which a fixture cannot provide. Everything else uses the paperless_dirs
+    fixture.
+    """
+    from documents.search import reset_backend
+
+    with TemporaryDirectory(ignore_cleanup_errors=True) as tmp:
+        dirs = build_paperless_dirs(Path(tmp))
+        with override_settings(**dirs_settings(dirs)):
+            reset_backend()
+            try:
+                yield dirs
+            finally:
+                reset_backend()