fix: read recalbox mandatory per named core

An element lists its cores. Its mandatory flag now follows whether those
cores need the file, and stays as written where none of them reads it.
cdi/cdibios.zip keeps mandatory=false (same_cdi does not read it), the
two amiberry kickstarts keep theirs, saturn_bios.bin becomes optional
for the three HLE cores it names.

tests/test_exporters.py

@@ -1141,6 +1141,34 @@ class RecalboxExport(unittest.TestCase):
         self.assertEqual({k: v for k, v in after.items() if k in before}, before)
         self.assertEqual(set(after) - set(before), set())
 
+    def test_mandatory_follows_the_cores_the_element_names(self):
+        """cdi/cdibios.zip names libretro/same_cdi, which does not read the
+        set: MAME requiring it says nothing about that element."""
+        scraped = {"systems": {"philips-cdi": {"native_id": "cdi", "files": [
+            {"name": "cdibios.zip", "destination": "cdi/cdibios.zip", "md5": "a" * 32,
+             "native_system": "cdi", "core": "libretro/same_cdi", "required": False},
+            {"name": "cdimono1.zip", "destination": "cdi/cdimono1.zip", "md5": "b" * 32,
+             "native_system": "cdi", "core": "libretro/same_cdi", "required": False},
+        ]}}}
+        truth = {"systems": {"philips-cdi": {"files": [
+            {"name": "cdibios.zip", "required": True, "_cores": ["mame0278"],
+             "_required_by": ["mame0278"]},
+            {"name": "cdimono1.zip", "required": True, "_cores": ["same_cdi", "mame0278"],
+             "_required_by": ["same_cdi"]},
+        ]}}}
+        systems, report = build_native_model(truth, scraped)
+        exporter = discover_exporters()["recalbox"]()
+        produced = exporter.render(systems, report, {}, None)["es_bios.xml"]
+        mandatory = {
+            b.get("path"): b.get("mandatory") for b in ET.fromstring(produced).iter("bios")
+        }
+        self.assertEqual(mandatory, {"cdi/cdibios.zip": "false", "cdi/cdimono1.zip": None})
+        changes = landed_changes(exporter, systems).records
+        self.assertEqual(
+            [(c["name"], c["old"], c["new"]) for c in changes],
+            [("cdimono1.zip", False, True)],
+        )
+
     def test_a_truncated_export_is_reported(self):
         exporter, systems, _ = self._render()
         empty = {