TensorForceField serialization

[mattwthompson]

Closes #168

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.47%. Comparing base (4db3654) to head (93909c6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
tyff/_serialization.py	96.29%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #178      +/-   ##
==========================================
+ Coverage   81.40%   81.47%   +0.07%     
==========================================
  Files          56       57       +1     
  Lines        5070     5097      +27     
==========================================
+ Hits         4127     4153      +26     
- Misses        943      944       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Copilot review overview

🟡 Changes recommended

The new module contains non-functional dead code (_Tensor and the sparse helpers) and the exceptions serialization path is entirely untested.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Add tests for exception serialization round-trip · New
• Remove unused tensor and sparse serialization helpers · New

What changed in this PR

This PR adds JSON serialization support for TensorForceField (closing #168). It introduces a new tyff/_serialization.py module providing dump_*/load_* functions that convert a TensorForceField (and its nested TensorPotential and TensorVSites) to and from plain Python dicts suitable for json.dump/json.load, handling tensors, units, OpenFF PotentialKeys, and exceptions. A new test module exercises round-trip serialization for a basic water force field and a virtual-site force field.

Changes:

• New tyff/_serialization.py with helpers to encode/decode tensors, units, potential keys, and exceptions, plus top-level dump_tensor_force_field/load_tensor_force_field.
• New tyff/_tests/test_serialization.py with a field-by-field comparison helper and two round-trip tests (basic and virtual sites).

File	Description
tyff/​_serialization.py	Adds dump/load functions for TensorForceField, TensorPotential, and TensorVSites, plus tensor/exception encoding helpers (includes some unused _Tensor/sparse helpers).
tyff/​_tests/​test_serialization.py	Adds round-trip serialization tests and a compare_tensor_force_fields helper (does not compare exceptions).

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.