fix(types): better return type

[henryiii]

For #161 CC @matthewfeickert

[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 0.01%.

Quality metrics	Before	After	Change
Complexity	13.11 🙂	13.11 🙂	0.00
Method Length	137.18 😞	137.00 😞	-0.18 👍
Working memory	16.13 ⛔	16.13 ⛔	0.00
Quality	38.24% 😞	38.25% 😞	0.01% 👍

Other metrics	Before	After	Change
Lines	410	408	-2

Changed files	Quality Before	Quality After	Quality Change
src/hist/plot.py	38.24% 😞	38.25% 😞	0.01% 👍

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
src/hist/plot.py	plot_pull	21 😞	699 ⛔	21 ⛔	18.34% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
src/hist/plot.py	plot2d_full	9 🙂	278 ⛔	14 😞	38.61% 😞	Try splitting into smaller methods. Extract out complex expressions
src/hist/plot.py	_curve_fit_wrapper	5 ⭐	156 😞	14 😞	50.72% 🙂	Try splitting into smaller methods. Extract out complex expressions
src/hist/plot.py	_expr_to_lambda	9 🙂	129 😞	11 😞	54.60% 🙂	Try splitting into smaller methods. Extract out complex expressions
src/hist/plot.py	plot_pie	1 ⭐	51 ⭐	10 😞	75.33% ⭐	Extract out complex expressions

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• 😞 poor
• ⛔ very poor

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