[FEA] [Multi-GPU Polars] Avoid GPU Requirement on Client During IR Lowering

## Avoid GPU Requirement on Client During IR Lowering

### Summary

The current design may require a GPU on the client during the IR lowering stage. Ideally, the client should not require a GPU.

### Problem

IR lowering (`lower_ir_graph`) is currently performed on the client, which can trigger GPU usage. This introduces an implicit requirement that the client machine has a GPU, even in distributed setups where all actual execution happens on workers.

### Proposed Direction

Move IR lowering from the client to the workers.

### Challenges

A naive approach, where each worker independently runs `lower_ir_graph`, would lead to redundant work:

* All workers would sample the same Parquet metadata and row groups.
* This is inefficient and may lead to unnecessary overhead.

cc. @rjzamora, @TomAugspurger