Fix nodiscard qualifier in Result class

[kononovk]

Purpose

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Related Information

• Design document: ...
• Bench PR: ...

Testing

• This change is a trivial rework or code cleanup without any test coverage.
• This change is already covered by existing tests.
• This PR adds tests that were used to verify all changes.
• There are tests in an external testing repository: ...

[coveralls]

Pull Request Test Coverage Report for Build 5099701493

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 5021008928:	0.0%
Covered Lines:	1602
Relevant Lines:	1602

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💛 - Coveralls

[codecov]

Codecov Report

Merging #241 (a2e7fdf) into main (92b9550) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #241   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           68        68           
  Lines         1598      1602    +4     
=========================================
+ Hits          1598      1602    +4     

Impacted Files	Coverage Δ
include/yaclib/util/result.hpp	100.00% <100.00%> (ø)

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[MBkkt]

I like the idea but I don't like the solution.
At the same time I don't know another solution.
So don't merge for now