Update doc expect messages in sync module following style guide

[Windolon]

Updates user-facing docs in the sync module following the style guide.

After issue #159751

This is my first time contributing to rust. Please tell me if there are any issues with my PR, and I'll try my best to fix it!

[rustbot]

Thanks for the pull request, and welcome! The Rust Project has assigned @JohnTitor (or someone else) to review your changes, you should hear from them (or someone else) within the next two weeks.

Please see the contribution instructions and our LLM policy for more information.

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @ChrisDenton, libs
• @ChrisDenton, libs expanded to 13 candidates
• Random selection from ChrisDenton, Darksonn, JohnTitor, Mark-Simulacrum

[JohnTitor]

@bors r+ rollup

View changes since this review

[rust-bors]

📌 Commit eaecaec has been approved by JohnTitor

It is now in the queue for this repository.

[rust-bors]

☀️ Test successful - CI
Approved by: JohnTitor
Duration: 3h 13m 58s
Pushing 98fd715 to main...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 0630f86 (parent) -> 98fd715 (this PR)

Test differences

Show 4 test diffs

4 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 98fd715edd3a0a5aa8f2041d7e20a3143b0fc0d3 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. test-x86_64-msvc-ext3: 1h 10m -> 1h 59m (+68.9%)
2. dist-x86_64-msvc-alt: 1h 50m -> 2h 57m (+61.4%)
3. test-x86_64-mingw-1: 1h 58m -> 3h 10m (+60.5%)
4. test-i686-gnu-nopt-1: 1h 33m -> 2h 11m (+40.6%)
5. test-x86_64-gnu-llvm-22-3: 1h 21m -> 1h 53m (+38.5%)
6. test-x86_64-gnu-stdlib-semver-check: 17m 20s -> 10m 49s (-37.6%)
7. dist-loongarch64-musl: 1h 23m -> 1h 54m (+37.1%)
8. test-x86_64-gnu-gcc-core-tests: 14m 39s -> 9m 52s (-32.7%)
9. test-pr-check-1: 41m 5s -> 27m 57s (-32.0%)
10. test-x86_64-gnu-llvm-22-2: 1h 46m -> 1h 12m (-31.8%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (98fd715): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.9%	[0.8%, 0.9%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.4%, 0.7%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-0.6%, -0.5%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-0.6%, 0.7%]	6

Cycles

Results (primary 0.2%, secondary 2.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.5%, 0.8%]	4
Regressions ❌ (secondary)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-0.8%	[-0.9%, -0.6%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-0.9%, 0.8%]	6

Binary size

Results (primary -0.0%, secondary -0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.0%	[-0.1%, -0.0%]	26
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	6
All ❌✅ (primary)	-0.0%	[-0.1%, -0.0%]	26

Bootstrap: 492.224s -> 492.1s (-0.03%)
Artifact size: 406.97 MiB -> 406.87 MiB (-0.02%)