As the title say, Is there a plugin for coding? Something like the standardnotes Code-Editor Extension?
Does it do anything extra other than syntax highlighting?
The main editor is codemirror and whilst it defaults to Markdown syntax highlighting it supports whatever you want in code fence blocks (surround in triple backticks) and has highlighting for most common languages.
```sql select thing from table where thing = other_thing
There is a plugin to turn on line numbers if you want that too.