Add parallelism to cloness_centrality (#1392)

* First look at parallel implementation

* Add parallel threshold parameter

* Add parllel_threshold to Python arguments

* Make weighted closeness centrality also parallel

* Add new argument to type stubs

* Document parameters for newman's type specific functions

* Add parallel tests to Python

* Add release notes for the change

* Boost coverage of Newman Weighted Centrality via unweighted test case

* Simplify implementation with .collect()

* Add parallel_threshold to docstring

* Fix cargo clippy warnings

* Document RAYON_NUM_THREADS

* Move reno section to upgrade

* Add rayon num threads detail to Python

* Update Python docstring as well

* Try to fix indentation

Author: IvanIsCoding

releasenotes/notes/parallel-closeness-centrality-5165f62e370181eb.yaml

@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    The :func:`~.closeness_centrality` method is now parallel for better performance.
+    The parallelism is toggled via the new `parallel_threshold` optional parameter.
+upgrade:
+  - |
+    The `closeness_centrality` function in `rustworkx-core`
+    now requires `parallel_threshold` parameter which controls when the
+    algorithm switches to parallel execution. This is a breaking change.