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.

scripts/export_native.py

@@ -509,7 +509,7 @@ def _added_fields(exporter: object, entry: object) -> dict:
     if "size" in carried and entry.size() is not None:
         written["size"] = entry.size()
     if "required" in carried:
-        written["required"] = entry.required
+        written["required"] = exporter.required_value(entry)
     return written
 
 
@@ -535,20 +535,24 @@ def landed_changes(exporter: object, systems: dict) -> LandedChanges:
                         "added", entry, None, None, _added_fields(exporter, entry)
                     ))
                 continue
+            if (
+                (entry.truth or {}).get("required") is not None
+                and entry.platform.get("required") is not None
+                and exporter.states(entry, "required")
+                and exporter.required_value(entry) != bool(entry.platform["required"])
+            ):
+                records.append(_change(
+                    "requirement_corrected", entry, "required",
+                    bool(entry.platform["required"]), exporter.required_value(entry),
+                ))
             for field_name in entry.corrections:
-                if not exporter.states(entry, field_name):
+                if field_name == "required" or not exporter.states(entry, field_name):
                     continue
-                if field_name == "required":
-                    records.append(_change(
-                        "requirement_corrected", entry, "required",
-                        bool(entry.platform.get("required")), entry.required,
-                    ))
-                else:
-                    records.append(_change(
-                        "hash_corrected", entry, field_name,
-                        _platform_value(entry, field_name),
-                        exporter.written(entry, field_name),
-                    ))
+                records.append(_change(
+                    "hash_corrected", entry, field_name,
+                    _platform_value(entry, field_name),
+                    exporter.written(entry, field_name),
+                ))
             records.extend(
                 _change("hash_filled", entry, field_name, None,
                         exporter.written(entry, field_name))