Update csharpier and reformat

[adamhathcock]

supersedes #1032

[Copilot]

Pull request overview

This PR updates the CSharpier code formatter from version 1.1.2 to 1.2.1 and applies its reformatting rules across test files in the codebase.

• Updates CSharpier tool version in dotnet-tools.json
• Reformats collection initializers to multi-line format with one element per line
• Applies consistent formatting across Xz, Rar, and Arj test files

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
.config/dotnet-tools.json	Updates CSharpier version from 1.1.2 to 1.2.1
tests/SharpCompress.Test/Xz/XZIndexTests.cs	Reformats byte array collection initializer to multi-line format
tests/SharpCompress.Test/Xz/XZIndexAsyncTests.cs	Reformats byte array collection initializer to multi-line format
tests/SharpCompress.Test/Rar/RarReaderTests.cs	Reformats string array collection initializers to multi-line format
tests/SharpCompress.Test/Rar/RarReaderAsyncTests.cs	Reformats string array collection initializers to multi-line format
tests/SharpCompress.Test/Arj/ArjReaderTests.cs	Reformats string array collection initializer to multi-line format

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