Reject NaN values in numeric inputs

[MaxGhenis]

Summary

• reject NaN values passed through simulation.set_input / holder input paths for numeric variables
• keep internal cache writes free of the new validation so calculated values are not newly blocked
• validate built-in period dispatch/divide input helper paths and add regressions for float and int inputs

Fixes #389.

TDD / verification

• Confirmed the new NaN regressions failed before the implementation.
• uv run --no-sync pytest tests/core/test_holders.py -q
• uv run --no-sync ruff check policyengine_core/holders/holder.py policyengine_core/holders/helpers.py tests/core/test_holders.py
• uv run --no-sync ruff format --check policyengine_core/holders/holder.py policyengine_core/holders/helpers.py tests/core/test_holders.py

Review

• Read-only subagent review requested before merge.