fix: update Python Rust example to use rust.toolchain()

Author: markovejnovic

examples/rust/.harmont/pipeline.py

@@ -7,7 +7,7 @@
 
 @hm.target()
 def project() -> RustToolchain:
-    return hm.rust(path=".")
+    return hm.rust.toolchain(path=".")
 
 
 @hm.pipeline(