libluna: Add assignment operators to Buffer

libluna/include/luna/Buffer.h

@@ -11,6 +11,9 @@ class Buffer
     Buffer(Buffer&& other);
     Buffer(const Buffer& other) = delete; // For now.
 
+    Buffer& operator=(Buffer&&);
+    Buffer& operator=(const Buffer&) = delete;
+
     static Result<Buffer> create_sized(usize size);
 
     Result<void> try_resize(usize new_size);

libluna/src/Buffer.cpp

@@ -15,6 +15,16 @@ Buffer::Buffer(Buffer&& other) : m_data(other.data()), m_size(other.size())
     other.m_data = nullptr;
 }
 
+Buffer& Buffer::operator=(Buffer&& other)
+{
+    if (&other == this) return *this;
+    if (m_data) free_impl(m_data);
+    m_data = other.m_data;
+    m_size = other.m_size;
+    other.m_data = nullptr;
+    return *this;
+}
+
 Buffer::~Buffer()
 {
     if (m_data) free_impl(m_data);