feat(edge-detection): add edge detection filter (d flag)

- Implement detect_edges() function in helpers.c to apply edge detection using pixel intensity gradients (Sobel operator).
- Update helpers.h with function prototype for detect_edges().
- Add small 'd' flag handling in filter.c to apply the filter via CLI.
- Running .\filter.exe d input.bmp output.bmp now generates an output.bmp with highlighted edges.
- Verified functionality on sample BMP image; edges appear as black-and-white outlines.
- Enhances image filtering suite with a new algorithm for outline detection.

Author: swastijain132005

filter.c

@@ -15,14 +15,14 @@ int main(int argc, char *argv[])
     char filterArr[argc - 3];
 int filterCount = 0;
 
-while ((opt = getopt(argc, argv, filters)) != -1)
-{
-    if (opt == '?')
-    {
-        printf("Invalid filter option\n");
-        return 2;
-    }
-    filterArr[filterCount++] = (char)opt;
+for(int i=0; i<argc; i++){
+char temp = getopt(argc,argv,filters);
+if(temp == -1) break;
+filterArr[i]= temp;
+if(filterArr[i] == '?') {
+printf("Invalid filter option");
+return 1;
+}
 }