xugrid: baseline integration with circle example (#294)

* Add xugrid-backed reading of MODFLOW 6 binary output for both structured (DIS) and vertex (DISV) grids
* Refactor the UGRID mesh topology generation for NetCDF input writing
* Add circle.py and extend frenchman-flat.py example scripts to demonstrate DISV output reading and xugrid plotting

Author: mjreno

.gitignore

@@ -1,4 +1,5 @@
 build/
+docs/examples/circle/*
 docs/examples/frenchman-flat/*
 docs/examples/quickstart/*
 docs/examples/twri/*

.pre-commit-config.yaml

@@ -10,6 +10,7 @@ repos:
       exclude: ^test/__compare__|^docs/examples/data
     - id: check-yaml
     - id: check-added-large-files
+      args: ['--maxkb=2048']
     - id: check-toml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   rev: v0.8.2

docs/_toc.yml

@@ -10,6 +10,8 @@ parts:
         title: TWRI
       - file: examples/frenchman-flat
         title: Frenchman Flat
+      - file: examples/circle
+        title: Circle
 
   - caption: Developer Notes
     chapters: