gcc 15 and C23 force some union trickery on buffer.h :-(

add a few buffer_init*_forread variants to pretend we have type safety
  make sure buffer_init_staticcontents handles flushing attempts

buffer/buffer_init_read.c

@@ -3,7 +3,7 @@
 
 int buffer_init_read(buffer* b, int fd, char* y,size_t ylen) {
   if (fd==-1) return -1;
-  buffer_init(b, read, fd, y, ylen);
+  buffer_init_forread(b, read, fd, y, ylen);
   return 0;
 }