Type Conversion: Silent Failures

Conversion methods return default values on failure, making debugging impossible:

```js
"invalid".to_i()  // Returns 0 (can't distinguish from actual 0)
"abc".to_f()      // Returns 0.0
nil.to_s()        // Returns ""
```
**Recommendation:**
- Return ERROR object on failure
  ```js
  result = "abc".to_i()
  if result.type() == "ERROR"
    puts("Conversion failed: " + result.message())
  end
  ```