feat: list recalbox cores per board

Recalbox builds seven board images with different emulators. The new
target scraper reads each board's defconfig against the package every
system.ini core names. The names that reached no profile are mapped to
the projects Recalbox builds or profiled from their source, and the
mupen64plus video plugins are set aside.

tests/test_target_scrapers.py

@@ -233,6 +233,40 @@ class RocknixPerDevice(unittest.TestCase):
                          ["ecwolf-lr", "prboom-lr", "vitaquake3-lr"])
 
 
+class RecalboxPerBoard(unittest.TestCase):
+    """Recalbox had no target list: a Raspberry Pi 3 pack carried the
+    firmware of emulators only its x86_64 image builds."""
+
+    SYSTEM_INI = (
+        "[core.0]\npackage = BR2_PACKAGE_PCSX2\nemulator = \"pcsx2\"\ncore = \"pcsx2\"\n"
+        "[core.1]\npackage = BR2_PACKAGE_LIBRETRO_PCSX_REARMED\nemulator = \"libretro\"\n"
+        "core = \"pcsx_rearmed\"\npackage.rpi3 = BR2_PACKAGE_LIBRETRO_PCSX_REARMED_NEON\n"
+        "[core.2]\npackage = BR2_PACKAGE_LIBRETRO_SWANSTATION\nemulator = \"libretro\"\n"
+        "core = \"swanstation\"\n"
+        "[core.2.rpi3]\npackage = BR2_PACKAGE_LIBRETRO_DUCKSTATION\nemulator = \"libretro\"\n"
+        "core = \"duckstation\"\n"
+    )
+
+    def test_a_board_gets_the_cores_its_defconfig_builds(self):
+        from scraper.recalbox_scraper import board_cores  # noqa: PLC0415
+        from scraper.targets.recalbox_targets_scraper import (  # noqa: PLC0415
+            defconfig_arch,
+            enabled_packages,
+        )
+
+        x86 = enabled_packages("BR2_x86_64=y\nBR2_PACKAGE_PCSX2=y\n"
+                               "BR2_PACKAGE_LIBRETRO_PCSX_REARMED=y\n"
+                               "BR2_PACKAGE_LIBRETRO_SWANSTATION=y\n# BR2_PACKAGE_X is not set\n")
+        self.assertEqual(board_cores(self.SYSTEM_INI, "x86_64", x86),
+                         {"pcsx2", "pcsx_rearmed", "swanstation"})
+        rpi3 = enabled_packages("BR2_arm=y\nBR2_PACKAGE_LIBRETRO_PCSX_REARMED_NEON=y\n"
+                                "BR2_PACKAGE_LIBRETRO_DUCKSTATION=y\n")
+        self.assertEqual(board_cores(self.SYSTEM_INI, "rpi3", rpi3),
+                         {"pcsx_rearmed", "duckstation"})
+        self.assertEqual(defconfig_arch("BR2_arm=y\n"), "armhf")
+        self.assertEqual(defconfig_arch("BR2_aarch64=y\n"), "aarch64")
+
+
 class RetroPieModuleFlags(unittest.TestCase):
     """The RetroPie target list read flags as requirements and libretro alone.