chore: align project configuration with NuGet library template best practices (#53)

Compared TrxLib against the upstream [NuGet library
template](https://github.com/BenjaminMichaelis/DotnetTemplates/tree/main/templates/Library/NuGet)
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.

Author: BenjaminMichaelis

.editorconfig

@@ -26,8 +26,8 @@ indent_size = 4
 tab_width = 4
 
 # New line preferences
-end_of_line = crlf
-insert_final_newline = false
+end_of_line = lf
+insert_final_newline = true
 
 #### .NET Coding Conventions ####
 [*.{cs,vb}]

.gitattributes

@@ -0,0 +1,35 @@
+# Auto normalize line endings for all tracked files
+* text=auto
+
+# Explicitly normalize to LF for text files
+*.cs text eol=lf
+*.csproj text eol=lf
+*.props text eol=lf
+*.targets text eol=lf
+*.sln text eol=lf
+*.slnx text eol=lf
+*.md text eol=lf
+*.json text eol=lf
+*.xml text eol=lf
+*.yml text eol=lf
+*.yaml text eol=lf
+*.config text eol=lf
+*.editorconfig text eol=lf
+*.gitignore text eol=lf
+*.gitattributes text eol=lf
+
+# Binary files
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.mov binary
+*.mp4 binary
+*.mp3 binary
+*.gz binary
+*.zip binary
+*.7z binary
+*.ttf binary
+*.otf binary
+*.fnt binary

Directory.Build.props

@@ -11,7 +11,7 @@ See: https://learn.microsoft.com/visualstudio/msbuild/customize-your-build
   <PropertyGroup>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
-    <LangVersion>13.0</LangVersion>
+    <LangVersion>14</LangVersion>
     <!-- 
     If you you like to see source generated files saved to disk you can enable the following:
     https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/source-generators-overview
@@ -42,6 +42,7 @@ See: https://learn.microsoft.com/visualstudio/msbuild/customize-your-build
      <PackageProjectUrl>https://github.com/BenjaminMichaelis/TrxLib</PackageProjectUrl> 
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageRequireLicenseAcceptance>true</PackageRequireLicenseAcceptance>
+    <PackageTags>trx;test-results;xml;parser</PackageTags>
   </PropertyGroup>
 
   <PropertyGroup Label="SourceLink">

Directory.Packages.props

@@ -11,6 +11,7 @@
   <!-- This property enables the Central Package Management feature -->
   <PropertyGroup>
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
+    <CentralPackageTransitivePinningEnabled>true</CentralPackageTransitivePinningEnabled>
   </PropertyGroup>
   <!--
   This defines the set of centrally managed packages.