test: add equal-objects-equal-hash tests and enforce static: dict[str…

[Adityakk9031]

Closes #30

Summary

Follow-up to #26 closing the two hashability gaps identified in #30:

1. Equal-Objects-Equal-Hash Invariant: Updated test_instances_and_realizations_are_hashable to construct two independent but value-equal instances/realizations (a == b), asserting hash(a) == hash(b) and dict key lookup {a: "x"}[b] == "x". This guards against identity-hashing regressions.
2. Tightened static Field Type: Changed TaskInstance.static annotation from dict[str, Any] to dict[str, Scalar] (hashable scalars only) so unhashable structures (e.g. lists) cannot be inserted into static.
3. Spec-Wide Hashing Verification: Added an assertion loop traversing all task instances across SPECS to verify hash(instance) succeeds for all 50 instances.

Changes

• instances.py: Tightened static field type annotation from dict[str, Any] to dict[str, Scalar].
• embodiment.py: Typed _render() return signature as np.ndarray[Any, Any] to satisfy mypy generic requirements.
• test_instances.py: Added equal-object hash checks, dict lookup assertions, and spec-wide SPECS hash iteration.

Verification

• pytest --cov passed 377/377 tests with 100.00% statement & branch coverage.
• ruff check . & ruff format --check . passed cleanly.
• mypy strict type checking passed with 0 issues.

[Adityakk9031]

@jeqcho have a look

[jeqcho]

Thanks for this. Hashing every spec in SPECS rather than a sample is what makes the invariant hold for specs nobody has written yet.