[mipi_spi] Cache code generation across display tests

The native.yaml and lvgl.yaml fixtures are each compiled twice; once by
the codegen assertions in test_init.py and once by the metadata
assertions in test_display_metadata.py. Add a session scoped cache so
each fixture is generated once, with the resulting main.cpp text and a
snapshot of the display metadata reused across tests. CI hits the
duplicated tests in well under 10ms instead of paying the full
generation cost a second time.

tests/component_tests/mipi_spi/conftest.py

@@ -1,11 +1,13 @@
 """Tests for mpip_spi configuration validation."""
 
 from collections.abc import Callable, Generator
+from pathlib import Path
 from unittest import mock
 
 import pytest
 
 from esphome import config_validation as cv
+from esphome.components.display import DisplayMetaData, get_all_display_metadata
 from esphome.components.esp32 import KEY_ESP32, KEY_VARIANT, VARIANTS
 from esphome.components.esp32.gpio import validate_gpio_pin
 from esphome.const import CONF_INPUT, CONF_OUTPUT
@@ -23,6 +25,40 @@ def mock_spi_final_validate():
         yield
 
 
+@pytest.fixture(scope="session")
+def _generation_cache() -> dict[Path, tuple[str, dict[str, DisplayMetaData]]]:
+    """Session-wide cache of generation output keyed by fixture yaml path.
+
+    Stores ``(main_cpp_text, display_metadata_snapshot)`` so multiple tests
+    that exercise the same fixture only pay for code generation once.
+    """
+    return {}
+
+
+@pytest.fixture
+def cached_generate_main(
+    generate_main: Callable[[str | Path], str],
+    _generation_cache: dict[Path, tuple[str, dict[str, DisplayMetaData]]],
+) -> Callable[[Path], tuple[str, dict[str, DisplayMetaData]]]:
+    """Like ``generate_main`` but caches results across the test session.
+
+    Returns ``(main_cpp_text, display_metadata_snapshot)``; the snapshot is
+    captured at generation time so callers see the same data after CORE has
+    been reset for the next test.
+    """
+
+    def _get(path: Path) -> tuple[str, dict[str, DisplayMetaData]]:
+        path = Path(path)
+        cached = _generation_cache.get(path)
+        if cached is None:
+            main_cpp = generate_main(path)
+            cached = (main_cpp, dict(get_all_display_metadata()))
+            _generation_cache[path] = cached
+        return cached
+
+    return _get
+
+
 @pytest.fixture
 def choose_variant_with_pins() -> Generator[Callable[[list], None]]:
     """

tests/component_tests/mipi_spi/test_display_metadata.py

@@ -173,12 +173,11 @@ def test_metadata_multiple_displays_independent(
 
 
 def test_metadata_via_code_generation_native(
-    generate_main: Callable[[str | Path], str],
+    cached_generate_main: Callable[[Path], tuple[str, dict[str, DisplayMetaData]]],
     component_fixture_path: Callable[[str], Path],
 ) -> None:
     """Full code generation for native.yaml should produce correct metadata."""
-    generate_main(component_fixture_path("native.yaml"))
-    all_meta = get_all_display_metadata()
+    _, all_meta = cached_generate_main(component_fixture_path("native.yaml"))
     # native.yaml: model JC3636W518 -> 360x360, no writer, full hardware rotation
     assert len(all_meta) == 1
     meta = next(iter(all_meta.values()))
@@ -188,12 +187,11 @@ def test_metadata_via_code_generation_native(
 
 
 def test_metadata_via_code_generation_lvgl(
-    generate_main: Callable[[str | Path], str],
+    cached_generate_main: Callable[[Path], tuple[str, dict[str, DisplayMetaData]]],
     component_fixture_path: Callable[[str], Path],
 ) -> None:
     """Full code generation for lvgl.yaml should produce correct metadata."""
-    generate_main(component_fixture_path("lvgl.yaml"))
-    all_meta = get_all_display_metadata()
+    _, all_meta = cached_generate_main(component_fixture_path("lvgl.yaml"))
     # lvgl.yaml: model ST7735 -> 128x160, no writer (lvgl draws directly), full hw rotation
     assert len(all_meta) == 1
     meta = next(iter(all_meta.values()))

tests/component_tests/mipi_spi/test_init.py

@@ -307,12 +307,12 @@ def test_all_predefined_models(
 
 
 def test_native_generation(
-    generate_main: Callable[[str | Path], str],
+    cached_generate_main: Callable[[Path], tuple[str, dict[str, Any]]],
     component_fixture_path: Callable[[str], Path],
 ) -> None:
     """Test code generation for display."""
 
-    main_cpp = generate_main(component_fixture_path("native.yaml"))
+    main_cpp, _ = cached_generate_main(component_fixture_path("native.yaml"))
     assert (
         "mipi_spi::MipiSpiBuffer<uint16_t, mipi_spi::PIXEL_MODE_16, true, mipi_spi::PIXEL_MODE_16, mipi_spi::BUS_TYPE_QUAD, 360, 360, 0, 1, 0, true, 1, 1>()"
         in main_cpp
@@ -323,12 +323,12 @@ def test_native_generation(
 
 
 def test_lvgl_generation(
-    generate_main: Callable[[str | Path], str],
+    cached_generate_main: Callable[[Path], tuple[str, dict[str, Any]]],
     component_fixture_path: Callable[[str], Path],
 ) -> None:
     """Test LVGL generation configuration."""
 
-    main_cpp = generate_main(component_fixture_path("lvgl.yaml"))
+    main_cpp, _ = cached_generate_main(component_fixture_path("lvgl.yaml"))
     assert (
         "mipi_spi::MipiSpi<uint16_t, mipi_spi::PIXEL_MODE_16, true, mipi_spi::PIXEL_MODE_16, mipi_spi::BUS_TYPE_SINGLE, 128, 160, 0, 0, 0, true>();"
         in main_cpp