refactor(allocator): improve safety of String::from_utf8_unchecked

[overlookmotel]

Follow-on after #9656. Add a defence against potential double-free bug in String::from_utf8_unchecked.

As noted in the comment, this is probably unnecessary, but it doesn't hurt to add this defensive code while new Vec implementation is under development. We can remove it again later when we're satisfied we have covered all bases.

[overlookmotel]

• refactor(allocator): improve safety of String::from_utf8_unchecked #9772 👈 (View in Graphite)
• refactor(allocator/vec): add comment about lifetime bound on CloneIn for Vec #9771
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #9772 will create unknown performance changes

_{Comparing 03-14-refactor_allocator_improve_safety_of_string_from_utf8_unchecked_ (d13817e) with main (a1a8b93)}

Summary

🆕 33 new benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
🆕	codegen[checker.ts]	N/A	22.6 ms	N/A
🆕	codegen_sourcemap[checker.ts]	N/A	65.7 ms	N/A
🆕	isolated-declarations[vue-id.ts]	N/A	57.6 ms	N/A
🆕	lexer[RadixUIAdoptionSection.jsx]	N/A	20.9 µs	N/A
🆕	lexer[antd.js]	N/A	24.1 ms	N/A
🆕	lexer[cal.com.tsx]	N/A	5.7 ms	N/A
🆕	lexer[checker.ts]	N/A	14.5 ms	N/A
🆕	lexer[pdf.mjs]	N/A	3.8 ms	N/A
🆕	linter[RadixUIAdoptionSection.jsx]	N/A	2.7 ms	N/A
🆕	linter[cal.com.tsx]	N/A	1.2 s	N/A
🆕	linter[checker.ts]	N/A	3 s	N/A
🆕	mangler[antd.js]	N/A	15.9 ms	N/A
🆕	mangler[react.development.js]	N/A	293.1 µs	N/A
🆕	mangler[typescript.js]	N/A	39.4 ms	N/A
🆕	minifier[antd.js]	N/A	163.8 ms	N/A
🆕	minifier[react.development.js]	N/A	1.8 ms	N/A
🆕	minifier[typescript.js]	N/A	289.4 ms	N/A
🆕	estree[checker.ts]	N/A	87.4 ms	N/A
🆕	parser[RadixUIAdoptionSection.jsx]	N/A	91.5 µs	N/A
🆕	parser[antd.js]	N/A	113.4 ms	N/A
...	...	...	...	...

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

[Dunqing]

Merge activity

• Mar 14, 2:44 AM EDT: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Mar 14, 2:44 AM EDT: A user added this pull request to the Graphite merge queue.
• Mar 14, 2:56 AM EDT: A user merged this pull request with the Graphite merge queue.

[Dunqing]

You handle "unsafe" with great rigor; I am learning from you by observing closely.

[overlookmotel]

You handle "unsafe" with great rigor; I am learning from you by observing closely.

I am just following the greater minds of the authors of the std lib!