change: sort stylish issues; test only exported formatter functions

[alexandear]

Replace existing tests that target unexported formatter functions with tests for exported.

Sort issues by files in stylish for consistency. Remove trailing whitespace.

Updates #1362

[Copilot]

Pull request overview

This PR refactors the formatter package tests to follow black-box testing principles by testing the exported Format() method of each formatter rather than unexported helper functions like printStatistics() and table(). The change aligns with Go best practices of testing public APIs and makes tests more resilient to internal implementation changes.

• Removes tests for unexported printStatistics and table functions from formatter/friendly_test.go
• Updates formatter/formatter_test.go to test all formatters through their public Format() method with realistic failure data
• Adds github.com/google/go-cmp dependency for better diff output in test failures
• Removes the testpackage linter exception for the formatter package in .golangci.yml, enabling black-box testing

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
go.mod	Adds google/go-cmp v0.7.0 dependency for improved test assertions
go.sum	Updates dependency checksums for google/go-cmp
formatter/friendly_test.go	Removes white-box tests of unexported formatter helper functions
formatter/formatter_test.go	Refactors to test all formatters via their exported Format() method with more comprehensive test data including multiple failures and severity levels
.golangci.yml	Removes testpackage linter exception, enabling black-box testing for formatter package

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 5 changed files in this pull request and generated no new comments.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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