fix: pack_to_unchecked on big-endian targets

[clabby]

Overview

Fixes an issue for big-endian targets that was introduced by #32, where the temporary value created by as_le_slice was dropped immediately after the expression is evaluated. This change extends the lifetime of the Owned variant.

Repro (run miri): https://play.rust-lang.org/?version=stable&mode=release&edition=2024&gist=b92df156a14b6af538531bd8e3d28923

[codspeed-hq]

CodSpeed Performance Report

Merging #35 will degrade performances by 20.92%

_{Comparing clabby:cl/pack-fix (0b24fb4) with main (7f36b9c)}

Summary

⚡ 44 improvements
❌ 7 regressions
✅ 60 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	ends_with[16]	342.2 ns	432.8 ns	-20.92%
❌	ends_with[8]	339.7 ns	398.1 ns	-14.65%
❌	extend[16]	383.9 ns	471.4 ns	-18.56%
❌	extend[32]	350.6 ns	438.1 ns	-19.97%
❌	extend[8]	386.7 ns	474.2 ns	-18.45%
⚡	first[16]	120.3 ns	91.1 ns	+32.01%
⚡	first[32]	120.3 ns	91.1 ns	+32.01%
⚡	first[64]	120.3 ns	91.1 ns	+32.01%
⚡	first[8]	120.3 ns	91.1 ns	+32.01%
❌	get_byte_unchecked[16]	250 ns	279.2 ns	-10.45%
❌	get_byte_unchecked[8]	194.4 ns	223.6 ns	-13.04%
⚡	increment[16]	365.8 ns	307.5 ns	+18.97%
⚡	increment[32]	365.8 ns	307.5 ns	+18.97%
⚡	increment[64]	365.8 ns	307.5 ns	+18.97%
⚡	increment[8]	365.8 ns	307.5 ns	+18.97%
⚡	join[64]	276.7 ns	218.3 ns	+26.72%
⚡	last[16]	152.2 ns	123.1 ns	+23.7%
⚡	last[32]	152.2 ns	123.1 ns	+23.7%
⚡	last[8]	152.2 ns	123.1 ns	+23.7%
⚡	pack[16]	468.3 ns	410 ns	+14.23%
...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

[DaniPopes]

Thanks!