fs_lock:Check the nwaiter when deleting a bucket

[crafcat7]

Summary

Fixed the problem of releasing the bucket prematurely in multi-threaded flock scenarios by #13821

How to reproduce the problem
A thread setlk
B thread setlk_wait
A thread releases lock but fails to determine if nwaiter causes the bucket to be released prematurely post B thread causes crash due to heap use after free

Impact

Is a new feature added?: NO
Impact on build: NO
Impact on hardware: NO, this change does not specifically target any particular hardware architectures or boards.
Impact on documentation: NO,This patch does not introduce any new features
Impact on compatibility: This implementation aims to be backward compatible. No existing functionality is expected to be broken.

Testing

Build Host(s): Linux x86
Target(s): sim/nsh

We can through the two process USES case to verify the problem as follows

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/file.h>

#define FILENAME "/data/lockfile.txt"

int main() {
    int fd;

    fd = open(FILENAME, O_CREAT | O_RDWR, 0666);
    if (fd == -1) {
        perror("Failed to open file");
        exit(EXIT_FAILURE);
    }

    printf("Main thread: Trying to acquire write lock...\n");
    if (flock(fd, LOCK_EX) == -1) {
        perror("Failed to acquire write lock");
        close(fd);
        exit(EXIT_FAILURE);
    }
    printf("Main thread: Acquired write lock, holding for 5 seconds...\n");
    sleep(5);

    printf("Main thread: Releasing write lock...\n");
    if (flock(fd, LOCK_UN) == -1) {
        perror("Failed to release write lock");
        close(fd);
        exit(EXIT_FAILURE);
    }

    close(fd);
    printf("All locks released and file closed.\n");

    return 0;
}