feat(core/rust/ui): implement Clone for StrBuffer

[no changelog]

core/embed/rust/src/micropython/buffer.rs

@@ -20,6 +20,7 @@ use super::ffi;
 /// The `off` field represents offset from the `ptr` and allows us to do
 /// substring slices while keeping the head pointer as required by GC.
 #[repr(C)]
+#[derive(Clone)]
 pub struct StrBuffer {
     ptr: *const u8,
     len: u16,