fix(build): Include build.rs in published crates

This fixes a very niche build problem: depending on datafusion-python as
an rlib, and then attempting to build on macOS.

Because of the presence of an 'include' configuration in Cargo.toml,
everything else is excluded - including build.rs, which means the
necessary pyo3 linker flags aren't set.

Author: colinmarc

Cargo.toml

@@ -26,7 +26,7 @@ readme = "README.md"
 license = "Apache-2.0"
 edition = "2021"
 rust-version = "1.78"
-include = ["/src", "/datafusion", "/LICENSE.txt", "pyproject.toml", "Cargo.toml", "Cargo.lock"]
+include = ["/src", "/datafusion", "/LICENSE.txt", "build.rs", "pyproject.toml", "Cargo.toml", "Cargo.lock"]
 
 [features]
 default = ["mimalloc"]