docs: Add C++ unordered_set::cbegin() term entry (#8031) (#8034)

* docs: Add C++ unordered_set::cbegin() term entry (#8031)

* content fixes

* Update cbegin.md

* Update cbegin.md

* Remove std:: prefix in examples and explanations

* Update cbegin.md

* Format fix

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Author: Rishabh1925

content/cpp/concepts/unordered-set/terms/cbegin/cbegin.md

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+---
+Title: 'cbegin()'
+Description: 'Returns a constant iterator pointing to either the first element of the unordered set or the first element in a specific bucket.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'Iterators'
+  - 'Sets'
+  - 'STL'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+The **`cbegin()`** method returns a constant iterator that points to the first element of an [`unordered_set`](https://www.codecademy.com/resources/docs/cpp/unordered-set). A constant iterator allows read-only access to elements and prevents modification. Because `unordered_set` does not maintain any defined order, the element returned by `cbegin()` depends on its internal hash table structure.
+
+## Syntax
+
+```pseudo
+unordered_set_name.cbegin(n);
+```
+
+**Return value:**
+
+Returns a `const_iterator` (constant iterator) pointing to the first element in the `unordered_set`.
+
+Or, alternatively:
+
+```pseudo
+unordered_set_name.cbegin(n);
+```
+
+**Parameters:**
+
+- `n` (size_type): The bucket index. Must be less than `bucket_count()`.
+
+**Return value:**
+
+A `const_local_iterator` pointing to the first element in bucket `n`. If the bucket is empty, the returned iterator equals `cend(n)`.
+
+## Example
+
+This example demonstrates obtaining the starting element of an `unordered_set` using `cbegin()`:
+
+```cpp
+#include <iostream>
+#include <string>
+#include <unordered_set>
+using namespace std;
+
+int main() {
+  unordered_set<int> unique_numbers = {10, 5, 20, 15};
+
+  auto it = unique_numbers.cbegin();
+
+  cout << "The first element in internal order is: " << *it << "\n";
+
+  ++it;
+  if (it != unique_numbers.cend()) {
+    cout << "The second element is: " << *it << "\n";
+  }
+
+  // *it = 99; // Error: cannot modify through const_iterator
+
+  return 0;
+}
+```
+
+A sample output of this code is:
+
+```shell
+The first element in the set's internal order is: 20
+The second element is: 5
+```
+
+> **Note:** Attempting to modify the element pointed to by the `const_iterator` would result in a compilation error.
+
+## Codebyte Example
+
+In this example, the code retrieves a constant iterator for a specific bucket in the `unordered_set` and prints all elements stored in that bucket:
+
+```codebyte/cpp
+#include <iostream>
+#include <unordered_set>
+using namespace std;
+
+int main() {
+  unordered_set<string> words = {"cat", "dog", "rabbit", "lion"};
+
+  size_t bucket = 0;
+
+  auto it = words.cbegin(bucket);
+  auto end = words.cend(bucket);
+
+  cout << "Elements in bucket " << bucket << ":\n";
+
+  for (; it != end; ++it) {
+    cout << "  " << *it << "\n";
+  }
+
+  return 0;
+}
+```