[configoptional] Allow wrapping scalar values

[evan-bradley]

Description

Allow configoptional.Optional to wrap scalar values using new interfaces designed specifically to handle similar wrappers around scalar values.

Follow up to #13524.

[evan-bradley]

Leaving in draft while I resolve a bunch of rebase issues and prepare follow-up PRs to show this in use.

[jade-guiton-dd]

Some first reactions

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 7 untouched benchmarks
⏩ 76 skipped benchmarks¹

---

_{Comparing evan-bradley:configoptional-scalars-revived (2048001) with main (495f2c5)}

Footnotes

1. 76 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

❌ Patch coverage is 87.20930% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.19%. Comparing base (91b32ef) to head (2048001).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
confmap/internal/scalar.go	88.88%	3 Missing and 2 partials ⚠️
config/configoptional/optional.go	90.00%	1 Missing and 1 partial ⚠️
confmap/internal/marshaloption.go	66.66%	1 Missing and 1 partial ⚠️
confmap/internal/unmarshaloption.go	66.66%	1 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (87.20%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15175      +/-   ##
==========================================
- Coverage   91.23%   91.19%   -0.04%     
==========================================
  Files         703      705       +2     
  Lines       45902    45998      +96     
==========================================
+ Hits        41878    41950      +72     
- Misses       2820     2837      +17     
- Partials     1204     1211       +7     

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[mx-psi]

This looks reasonable to me and I think we have enough leeway to modify things that I feel comfortable moving forward with it now

[evan-bradley]

I looked this over again and I think it's ready for a review now.

[jade-guiton-dd]

The approach seems good overall

[jade-guiton-dd]

Almost good, mostly just nits, just one concern about the behavior of scalarValue.Marshal(nil)

[jade-guiton-dd]

Sorry for all the nitpicks, good work!

[evan-bradley]

Thank you! And really appreciate your careful reviews, your points led to a lot of meaningful improvements.

[mx-psi]

Re-approving after reading the convo above, thanks Jade for the careful review ❤️