Clarify example in Pin::new_unchecked docs

[fzs111]

This example in the docs of Pin::new_unchecked puzzled me for a relatively long time. Now I understand that it comes down to the difference between dropping the Pin vs dropping the pinned value.

I have extended the explanation to highlight this difference. In my opinion it is clearer now, and I hope it helps others understand Pin better.

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Mark-Simulacrum (or someone else) soon.

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[fzs111]

@rustbot label A-docs

[Mark-Simulacrum]

Happy to approve with commits squashed.

[fzs111]

@Mark-Simulacrum I squashed them.

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit 0f248d8 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

⌛ Testing commit 0f248d8 with merge 8c04c06...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 8c04c06 to master...

[rust-timer]

Finished benchmarking commit (8c04c06): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.6%	[-4.2%, -3.0%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.6%	[-4.2%, -3.0%]	2

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 631.647s -> 630.411s (-0.20%)
Artifact size: 317.29 MiB -> 317.18 MiB (-0.03%)