Add Hydrus-1D example and test case

[gerlero]

No description provided.

[Copilot]

🟡 Changes recommended

The new test imports frontx.examples.data.hydrus, which currently imports optional Matplotlib at module import time and will fail in a minimal test install where frontx[examples] is not installed.

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Pull request overview

This PR adds a Hydrus-1D reference dataset and uses it to validate frontx.solve/sol.flux against Hydrus-produced water content and velocity fields.

Changes:

• Add a new regression test that compares frontx’s solution/flux to Hydrus-1D outputs at multiple times.
• Add a new Hydrus example script for plotting frontx vs Hydrus-1D fields.
• Add a packaged Hydrus-1D dataset loader (frontx.examples.data.hydrus) that parses Nod_Inf.out into r, t, theta, and velocity.

File summaries

File	Description
tests/test_solve.py	Adds a Hydrus-1D regression test for solution and flux vs reference data.
src/frontx/examples/hydrus.py	Adds an example script to plot frontx vs Hydrus-1D water content and velocity fields.
src/frontx/examples/data/hydrus/init.py	Adds a dataset loader that parses Hydrus-1D output into NumPy arrays.

Review details

• Files reviewed: 3/4 changed files
• Comments generated: 1
• Review effort level: Lite

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 68.96552% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.26%. Comparing base (ce09687) to head (b81bb29).

Files with missing lines	Patch %	Lines
src/frontx/examples/data/hydrus/__init__.py	68.96%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #107      +/-   ##
==========================================
- Coverage   86.55%   85.26%   -1.29%     
==========================================
  Files          13       14       +1     
  Lines         580      638      +58     
==========================================
+ Hits          502      544      +42     
- Misses         78       94      +16     

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