Connectivity benchmarks

[cmdupuis3]

This PR adds benchmarks for basic connectivity routines.

Helps with Issue #1196

Overview

This PR adds benchmarks for the pairwise connectivity routines (face, edge, node). Two of the nine are apparently unimplemented and are included as TODOs: node/node and edge/edge. We can delete them if they don't make sense.

Expected Usage

Waiting for merge to see real timings on larger grids on Glade, the smaller ones may be too small to sample reliably.

Run benchmarks with asv:

asv run --python=same --bench "bench_connectivity.Connectivity"

PR Checklist

General

• [ x ] An issue is linked created and linked
• [ x ] Add appropriate labels
• [ x ] Filled out Overview and Expected Usage (if applicable) sections

Testing

• [N/A] Adequate tests are created if there is new functionality
• [ x ] Tests cover all possible logical paths in your function
• [N/A] Tests are not too basic (such as simply calling a function and nothing else)

Documentation

• Docstrings have been added to all new functions
• Docstrings have updated with any function changes
• [N/A] Internal functions have a preceding underscore (_) and have been added to docs/internal_api/index.rst
• [N/A] User functions have been added to docs/user_api/index.rst