Collect source bytes from ParseCallback

> We could instead remove this check and collect the bytes similar to https://github.com/tree-sitter/py-tree-sitter/pull/343 but I don't know how much of a performance impact this will have. 

 _Originally posted by @ObserverOfTime in [#105](https://github.com/tree-sitter/java-tree-sitter/issues/105#issuecomment-2900443906)_