Evaluate hlint `smell` directives (function length / arity)

## Summary

Consider adding hlint `smell` thresholds for long functions and high-arity
functions.

## Motivation

Raised while assessing the config in #132. hlint supports
`- smell: {type: long functions, limit: N}` and
`{type: many arg functions, limit: N}`. Current lean is low value: functions
in the library are small, and the record constructors are wide by spec
necessity (`Collection` has 7 fields mandated by Collection+JSON), so a naive
arity limit risks false positives against spec-driven record widths — needs
checking whether `smell` counts constructor arity before adopting. Filed to
capture the evaluation instead of re-deriving it later.

## Scope

- Confirm whether `many arg functions` would flag spec-mandated record constructors.
- Decide whether any threshold adds signal worth the config.

## Acceptance criteria

- [ ] Decision recorded; if adopted, thresholds chosen and CI green.