test: improve coverage for builtin/show.mbt

**Disclaimer:** This PR was generated by an LLM agent as part of an experiment.

## Summary

```
coverage of `builtin/show.mbt`: 79.3% -> 89.7%
```

Author: rami3l

builtin/show_test.mbt

@@ -231,3 +231,13 @@ test "Show for Char" {
   inspect!('\''.to_string(), content="'")
   inspect!('\\'.to_string(), content="\\")
 }
+
+test "char show hex digits" {
+  inspect!('\x01', content="'\\x01'")
+  inspect!('\x0b', content="'\\x0b'")
+}
+
+test "char_special" {
+  inspect!('\r', content="'\\r'")
+  inspect!('\b', content="'\\b'")
+}