[rust] Port Java's typed Arrow column-vector pattern to scan path

[fresh-borzoni]

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Description

The Rust scan path skips Java's typed-vector layer (VectorizedColumnBatch / ArrowRowColumnVector). Two consequences:

• Top-level accessors do column.data_type() + downcast on every call.
• Nested get_row eagerly materializes the whole struct and copies every leaf string and blob.

Java does the type dispatch once at construction and accessors are zero-copy.

• typed dispatch: Add a TypedColumn enum + TypedBatch built once per ArrowReader from (RecordBatch, RowType), then ColumnarRow accessors become single-arm matches.
• lazy nested ROW: with recursive TypedColumn::Row, the materialized nested GenericRow can hold borrowed Cows over Arrow buffers - no leaf copy. We wish keep the current trait + parameterize ColumnarRow with a lifetime most probably.

Willingness to contribute

• I'm willing to submit a PR!