Does not support deeply nested anonymous C structs

[kbkpbot]

Describe the bug

V language currently lacks support for parsing and converting deeply nested anonymous C structures. When attempting to use V's C interoperability features with C header files containing multi-level nested anonymous structs, parsing errors occur.

related to issue #25788

Reproduction Steps

$ tree .
.
├── deep.h
├── deep.v
└── v.mod

1 directory, 3 files

touch v.mod

deep.h

#ifndef __DEEP_H__
#define __DEEP_H__

struct DeepStruct{
        int A1;
        struct {
                int A2;
                struct {
                       int A3;
                       struct {
                                int A4;
                       } S3;
                } S2;
        } S1;
};
#endif

deep.v

module main

#insert "@VMODROOT/deep.h"

struct C.DeepStruct {
        A1 int
        S1 struct {
                A2 int
                S2 struct {
                        A3 int
                        S3 struct {
                                A4 int
                        }
                }
        }
}

fn main() {
        x := C.DeepStruct{}
        dump(x)
}

Compile deep.v:

v deep.v

Expected Behavior

compile ok

Current Behavior

$ v deep.v
deep.v:9:3: error: struct embedding must be declared at the beginning of the struct body
    7 |     S1 struct {
    8 |         A2 int
    9 |         S2 struct {
      |         ~~
   10 |             A3 int
   11 |             S3 struct {

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.12 bf7f43f

Environment details (OS name and version, etc.)

V full version	V 0.4.12 bf7f43f
OS	linux, Ubuntu 24.04.3 LTS
Processor	8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-9700 CPU @ 3.00GHz
Memory	11.05GB/15.51GB
V executable	/media/HD/github/kbkpbot/v/v
V last modified time	2025-11-22 12:31:54
V home dir	OK, value: /media/HD/github/kbkpbot/v
VMODULES	OK, value: /home/mars/.vmodules
VTMP	OK, value: /tmp/v_1000
Current working dir	OK, value: /home/mars/v/bug/struct/x
Git version	git version 2.43.0
V git status	weekly.2025.46-75-gbf7f43f2-dirty
.git/config present	true
cc version	cc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
gcc version	gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
clang version	Ubuntu clang version 18.1.3 (1ubuntu1)
tcc version	tcc version 0.9.28rc 2025-02-13 HEAD@f8bd136d (x86_64 Linux)
tcc git status	thirdparty-linux-amd64 696c1d84
emcc version	N/A
glibc version	ldd (Ubuntu GLIBC 2.39-0ubuntu8.6) 2.39

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