Add Dart Map .cast() term entry (#8119)

* Add Dart Map .cast() term entry

* Clarify description of .cast() method

Updated the description to clarify that keys and values are cast to specified types.

* Update cast.md

---------

Author: Muntazir-sd

content/dart/concepts/map/terms/cast/cast.md

@@ -0,0 +1,58 @@
+---
+Title: '.cast()'
+Description: 'Returns a new map with the same entries but with keys and values cast to the specified types.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Dart'
+  - 'Map'
+  - 'Methods'
+CatalogContent:
+  - 'learn-dart'
+  - 'paths/computer-science'
+---
+
+In Dart, the **`.cast()`** method returns a new `Map` containing the same key–value pairs as the original map, but with the specified key and value types. The returned map performs runtime type checks when reading or writing entries. If a key or value does not match the specified types, a `TypeError` is thrown.
+
+This method is commonly used when working with dynamically typed maps that need to be treated as a map with specific types.
+
+## Syntax
+
+```pseudo
+mapVariable.cast<NewKeyType, NewValueType>()
+```
+
+`mapVariable` is the `Map` object whose entries are cast to new types.
+
+**Parameters:**
+
+- `NewKeyType`: The target key type to cast the map’s keys to.
+- `NewValueType`: The target value type to cast the map’s values to.
+
+**Return value:**
+
+Returns a new `Map<K, V>` view of the original map, where keys and values are cast to the specified types.
+
+## Example
+
+In this example, a dynamically typed map is cast to a `Map<String, int>` so its entries can be accessed with strong typing:
+
+```dart
+void main() {
+  Map<dynamic, dynamic> rawData = {
+    'Alice': 90,
+    'Bob': 85,
+  };
+
+  Map<String, int> scores = rawData.cast<String, int>();
+
+  print(scores);
+}
+```
+
+The output of this code is:
+
+```shell
+{Alice: 90, Bob: 85}
+```