CardContentProvider: Avoid eager materialization of search results

```kotlin
val rv = MatrixCursor(columns, cardIds.size)
```
This allocates memory for all matching rows up front and instantiates Card objects for every result before returning the cursor

I'm concerned that we're not streaming the results and we could OOM

This is a standard pattern in many other methods in the class.
_Originally posted by @david-allison in https://github.com/ankidroid/Anki-Android/pull/20175#discussion_r2739962880_