TODO: Optional inference of INI [Dimensions]

Goal

Allow ExprTk INI models to omit or relax [Dimensions] when num_states / num_inputs / num_outputs can be inferred from dx*, y*, and references to u* in expressions—while preserving a clear error surface for ambiguous files.

Why

• Reduces redundancy and copy-paste errors; dimensions must stay consistent with equations today by hand.
• Purely a frontend concern; IR shape unchanged.

Scope hints

• Conservative inference: max index from dxN, yN, and uN symbol references.
• Ambiguity or mismatch vs explicit [Dimensions] → ERROR with actionable message (policy TBD in ADR or design doc update).

References

• src/model_parser/frontends/exprtk_ini.py.
• docs/design/model-library-and-versioning.md §7.

Acceptance sketch

• Tests: models with inferred dimensions equivalent to current explicit examples.
• Doc update for INI grammar in frontend module docstring and design docs.