haku2: add stats + fix crash w uninit vm

crates/haku2/src/bytecode.zig

@@ -1,5 +1,6 @@
 const std = @import("std");
 const mem = std.mem;
+const log = std.log.scoped(.bytecode);
 
 /// NOTE: This must be mirrored in bytecode.rs.
 pub const Opcode = enum(u8) {
@@ -70,6 +71,8 @@ pub const Defs = struct {
             .num_tags = mem.count(u8, tags_string, "\n"),
         };
 
+        log.debug("parsed defs {*} tags {s}: {}", .{ defs_string, tags_string, d });
+
         return d;
     }