Support stripping leading/trailing whitespace from all CSV fields before validation

 
I tried setting `dialect={"skipInitialSpace": True}` but that only handles spaces after delimiters — not full trimming of values.

I would like to strip both leading and trailing whitespace from all fields **before validation**. For example:

```
" Alice " → "Alice"
"Bob " → "Bob"
```

What is the recommended way to do this across all fields in all resources? 

Thanks!
