fix(difference): Add missing readonly to parameter

[mass2527]

I guess that when supporting read-only arrays, the readonly keyword was mistakenly omitted from the difference parameter.

[vercel]

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (main@1b3d9be). Learn more about missing BASE report.
Report is 374 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main       #83   +/-   ##
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  Coverage        ?   100.00%           
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  Files           ?        51           
  Lines           ?       264           
  Branches        ?        30           
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  Hits            ?       264           
  Misses          ?         0           
  Partials        ?         0           

[codspeed-hq]

CodSpeed Performance Report

Merging #83 will degrade performances by 83.01%

_{Comparing mass2527:fix/difference (4e14949) with main (1b3d9be)}

Summary

⚡ 7 improvements
❌ 5 regressions
✅ 74 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	mass2527:fix/difference	Change
❌	lodash/difference	56.8 µs	334.4 µs	-83.01%
⚡	lodash/differenceWith	385.2 µs	349.2 µs	+10.32%
⚡	es-toolkit/intersection	7.2 ms	2.8 ms	×2.6
⚡	lodash/intersectionWith	246.6 µs	92.3 µs	×2.7
⚡	lodash/pick	379.4 µs	252 µs	+50.55%
⚡	lodash/shuffle	319.7 µs	43.1 µs	×7.4
❌	lodash/union	76.3 µs	232.5 µs	-67.19%
⚡	lodash/unionBy	230.1 µs	75.7 µs	×3
❌	lodash/unionWith	238.8 µs	369.6 µs	-35.39%
⚡	lodash/uniqBy	21.5 ms	17.7 ms	+21.22%
❌	lodash/zip	246.6 µs	378.2 µs	-34.79%
❌	lodash/zipWith	260.1 µs	377.6 µs	-31.11%

[raon0211]

Thanks!