When translating C structs that use bitfields, C2Rust generates Rust code using the BitfieldStruct derive macro and #[bitfield(...)] attributes from the c2rust_bitfields crate. However, the generated code does not include the required import:

use c2rust_bitfields::BitfieldStruct;

As a result, the generated Rust code fails to compile.
Reproducer

#include <stdio.h>
#include <stdint.h>

struct PacketHeader {
    uint8_t version : 3;
    uint8_t type : 2;
    uint8_t flags : 3;
    uint16_t sequence : 10;
    uint16_t length : 6;
};

int main(void) {
    struct PacketHeader h = {0};
    h.version = 5;
    h.sequence = 513;
    printf("version=%u sequence=%u\n", h.version, h.sequence);
    return 0;
}

Generated Rust (excerpt)

#[derive(Copy, Clone, BitfieldStruct)]
#[repr(C)]
pub struct PacketHeader {
    #[bitfield(padding)]
    pub c2rust_padding: [u8; 1],
    #[bitfield(name = "version", ty = "uint8_t", bits = "0..=2")]
    #[bitfield(name = "type_0", ty = "uint8_t", bits = "3..=4")]
    #[bitfield(name = "flags", ty = "uint8_t", bits = "5..=7")]
    #[bitfield(name = "sequence", ty = "uint16_t", bits = "16..=25")]
    #[bitfield(name = "length", ty = "uint16_t", bits = "26..=31")]
    pub version_type_0_flags_sequence_length: [u8; 3],
}

Compilation Error:

error: cannot find derive macro `BitfieldStruct` in this scope
   --> src/main.rs:16:23
    |
16 | #[derive(Copy, Clone, BitfieldStruct)]
   |                       ^^^^^^^^^^^^^^

error: cannot find attribute `bitfield` in this scope
   --> src/main.rs:19:7
    |
19 |     #[bitfield(padding)]

Expected Behavior
When generating Rust code that uses BitfieldStruct and #[bitfield], C2Rust should automatically emit the required import:

use c2rust_bitfields::BitfieldStruct;

so that the generated code compiles without manual modification.
Environment

• c2rust version: v0.21.0
• platform: Ubuntu 24.04
• Rust: nightly-2022-08-08
• Clang version: 17.0.6