chore: align project configuration with NuGet library template best practices

[BenjaminMichaelis]

Compared TrxLib against the upstream NuGet library template and applied the improvements that were missing.

Changes

• Transitive pinning (Directory.Packages.props): Enables CentralPackageTransitivePinningEnabled, which pins transitive dependencies to the versions declared in CPM. This prevents supply-chain surprises where a transitive upgrade quietly pulls in a vulnerable or breaking version.

• LangVersion 14 (Directory.Build.props): Updates from 13.0 to 14 to use the latest C# language features and match current template conventions.

• Line endings: CRLF -> LF (.editorconfig, .gitattributes): Switches end_of_line from crlf to lf for cross-platform consistency and cleaner Git diffs. Also enables insert_final_newline. A .gitattributes file is added to enforce normalization at the repo level.

• PackageTags (Directory.Build.props): Adds trx test-results xml parser so the package is discoverable on NuGet.org by relevant search terms.

Not changed

TrxLib's existing metadata (Title, Authors, Description, License, URLs, README) was already in excellent shape -- no changes needed there. IsTestProject=true was already set in the test csproj.

[Copilot]

Pull request overview

Aligns repository-level build and packaging configuration with the current NuGet library template conventions.

Changes:

• Enables central package transitive pinning.
• Updates C# language version to 14 and adds NuGet package tags.
• Adds Git line-ending normalization and updates EditorConfig newline preferences.

Reviewed changes

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

File	Description
Directory.Packages.props	Enables transitive pinning for centrally managed packages.
Directory.Build.props	Updates language version and package discovery metadata.
.gitattributes	Adds repository-level text/binary normalization rules.
.editorconfig	Updates newline and final-newline preferences.

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