bench: refactor to use string interpolation in assert/contains

[Amansingh0807]

Resolves a part of #8647.

Description

What is the purpose of this pull request?

This pull request:

• Refactors the JavaScript benchmark in @stdlib/assert/contains to use @stdlib/string/format for string interpolation instead of string concatenation when specifying the benchmark name

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: use string interpolation in JavaScript benchmarks for the benchmark name (tracking issue) #8647

Questions

Any questions for reviewers of this pull request?

No.

Other

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Changes made:

• Added @stdlib/string/format import to the MODULES section
• Replaced string concatenation pkg+':len='+len with format( '%s:len=%d', pkg, len )

Testing:
Ran the benchmark locally using node lib\node_modules\@stdlib\assert\contains\benchmark\benchmark.length.js and verified that:

• The benchmark executes successfully without errors
• The formatted benchmark names match the original output exactly (@stdlib/assert/contains:len=10, etc.)
• All 18 benchmark tests pass

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

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• Yes
• No

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• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

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@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
assert/contains	$\color{green}155/155$ $color{green}+100.00%$	$\color{green}18/18$ $color{green}+100.00%$	$\color{green}1/1$ $color{green}+100.00%$	$\color{green}155/155$ $color{green}+100.00%$

The above coverage report was generated for the changes in this PR.

[kgryte]

LGTM

[kgryte]

@Planeshifter We seem to be getting failing tests in the ESLint first-unit-test lint rule.

[kgryte]

As the CI failure does not come from changes introduced in this PR, I will go ahead and merge.