feat: add Dict.concat/diff, Dict!.merge!/remove!

crates/erg_compiler/lib/std/_erg_dict.py

@@ -1,2 +1,18 @@
 class Dict(dict):
-    pass
+    def concat(self, other):
+        return Dict({**self, **other})
+    def diff(self, other):
+        return Dict({k: v for k, v in self.items() if k not in other})
+    # other: Iterable
+    def extend(self, other):
+        self.update(other)
+    # other: Dict
+    def merge(self, other):
+        self.update(other)
+    def insert(self, key, value):
+        self[key] = value
+    def remove(self, key):
+        res = self.get(key)
+        if res != None:
+            del self[key]
+        return res