rust: define prelude

Add a module that will contain frequently used traits and
occasionally structs.  They can be included quickly with
"use qemu_api::prelude::*".

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/qemu-api/meson.build

@@ -21,6 +21,7 @@ _qemu_api_rs = static_library(
       'src/definitions.rs',
       'src/device_class.rs',
       'src/offset_of.rs',
+      'src/prelude.rs',
       'src/vmstate.rs',
       'src/zeroable.rs',
     ],

rust/qemu-api/src/lib.rs

@@ -7,6 +7,11 @@
 #[rustfmt::skip]
 pub mod bindings;
 
+// preserve one-item-per-"use" syntax, it is clearer
+// for prelude-like modules
+#[rustfmt::skip]
+pub mod prelude;
+
 pub mod c_str;
 pub mod cell;
 pub mod definitions;

rust/qemu-api/src/prelude.rs

@@ -0,0 +1,6 @@
+// Copyright 2024 Red Hat, Inc.
+// Author(s): Paolo Bonzini <pbonzini@redhat.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+pub use crate::cell::BqlCell;
+pub use crate::cell::BqlRefCell;