wip: working on extern in VM

- Feat: add writer externs writing fns
- Feat: add VM reader functions

src/vm/reader/vm_rd_sections_sz.c

@@ -0,0 +1,29 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include <vm/internals/reader.h>
+
+// Reader sizes section
+bool vm_rd_sections_sz(fzl_vm_reader_t *reader, FILE *fd)
+{
+  if (!reader || !fd)
+    return false;
+
+  bool ok = vm_rd_u16(fd, 1, (uint16_t *)&reader->consts_count);
+  if (!ok)
+    return false;
+
+  ok = vm_rd_u16(fd, 1, &reader->extern_libs_count);
+  if (!ok)
+    return false;
+
+  ok = vm_rd_u16(fd, 1, &reader->extern_types_count);
+  if (!ok)
+    return false;
+
+  ok = vm_rd_u16(fd, 1, &reader->extern_fns_count);
+  if (!ok)
+    return false;
+
+  ok = vm_rd_word(fd, 1, &reader->ops_count);
+  return ok;
+}