fix: preserve empty projection in read_table

[QuakeWang]

Problem

read_table(..., columns=[]) currently skips projection because the Python wrapper checks if columns:. This makes an explicit empty projection behave the same as columns=None, so the convenience API returns all columns instead of a zero-column table with the row count preserved.

Fix

Change the wrapper to call reader.project(columns) whenever columns is not None, preserving the existing three-state projection semantics:

• None: read all columns
• non-empty list: read selected columns
• empty list: read zero columns and preserve row count

Add a regression test for read_table(..., columns=[]).

[JingsongLi]

+1