runs out of memory with large html files

I get this quite often:

```
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 170964 bytes) in C:\wamp\www\dib\dropinbase\extensions\DIndent\src\Indenter.php on line 123
```

Start by inspecting extensions/DIndent/src/Indenter.php at line 123 and reproduce the failure with a large HTML file under the reported PHP memory limit. Trace the memory-heavy operation and verify that large inputs can be indented without exhausting the limit.

Written by the indexing model from the issue text.