Modernize library: target net8.0/net10.0, modern C# idioms, xUnit v3

[niemyjski]

Summary

• Drop netstandard2.0, target net8.0 and net10.0 LTS only
• Use Random.Shared instead of a static new Random() instance — thread-safe by default
• Replace RandomNumberGenerator.Create() + disposal with RandomNumberGenerator.Fill() static method
• Use ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual, ThrowIfLessThan, ThrowIfGreaterThan guard APIs everywhere instead of manual throw statements
• Add where T : struct, Enum constraint on GetEnum<T>() to eliminate runtime typeof(T).IsEnum check
• Use Math.Clamp instead of separate Math.Min/Math.Max in GetBool
• Rewrite UpperCaseFirstCharacter with stackalloc Span<char> for zero-allocation path
• Convert to file-scoped namespace, collection expressions, expression-bodied members, string interpolation
• Add nullable annotations to GetVersion parameters and EnumerableExtensions
• Enable nullable reference types and implicit usings
• Upgrade build packages: SourceLink 10.0.103, AsyncFixer 2.1.0, MinVer 7.0.0
• Use dynamic copyright year MSBuild expression: $([System.DateTime]::Now.ToString(yyyy))
• Upgrade test project to xUnit v3 with Microsoft Testing Platform (xunit.v3.mtp-v2 3.2.2, Foundatio.Xunit.v3 13.0.0-beta3)
• Add TestingPlatformDotnetTestSupport and new-test-runner: true for CI
• Restore test parallelization disabling via AssemblyInfo.cs
• Add codeql-analysis.yml, copilot-setup-steps.yml, global.json, AGENTS.md
• Update README with comprehensive usage examples (all snippets verified to compile clean)

Public API changes

• GetEnum<T>(): added where T : struct, Enum constraint — callers passing non-enum type arguments will now get a compile-time error instead of a runtime ArgumentException
• GetVersion(string, string): parameters are now nullable (string?) — callers passing null now behave consistently with empty string (defaults applied)
• EnumerableExtensions.Random<T>(): return type is now T? (was T) — callers must handle possible null

Test plan

• dotnet build Exceptionless.RandomData.slnx --configuration Release — 0 warnings, 0 errors (both net8.0 and net10.0)
• dotnet run --project test/Exceptionless.RandomData.Tests -f net8.0 — 4 tests pass
• dotnet run --project test/Exceptionless.RandomData.Tests -f net10.0 — 4 tests pass
• All README code snippets verified to compile with 0 warnings

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

This PR modernizes the Exceptionless.RandomData library by targeting .NET 8.0 and .NET 10.0 (dropping .NET Standard 2.0), adopting modern C# idioms, and upgrading to xUnit v3 with the Microsoft Testing Platform. The changes focus on using newer .NET APIs like Random.Shared, RandomNumberGenerator.Fill(), guard methods (ArgumentOutOfRangeException.ThrowIf*), and performance improvements with stackalloc Span<char>. The PR also enables nullable reference types, adds comprehensive README examples, and includes new documentation (AGENTS.md) and GitHub workflows.

Changes:

• Modernized to .NET 8.0/10.0 with nullable reference types, implicit usings, file-scoped namespaces, and collection expressions
• Replaced custom Random instance with Random.Shared and updated to use modern guard APIs and RandomNumberGenerator.Fill()
• Upgraded test infrastructure to xUnit v3 with Microsoft Testing Platform
• Updated build packages (SourceLink, AsyncFixer, MinVer) and added GitHub Actions workflows for CodeQL and Copilot setup

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Exceptionless.RandomData/RandomData.cs	Core library modernized with Random.Shared, guard APIs, stackalloc Span, nullable annotations, and expression-bodied members
test/Exceptionless.RandomData.Tests/RandomDataTests.cs	Tests updated to file-scoped namespace, collection expressions, and fixed String casing
test/Exceptionless.RandomData.Tests/Properties/AssemblyInfo.cs	Updated xUnit attribute name for test parallelization settings
test/Exceptionless.RandomData.Tests/Exceptionless.RandomData.Tests.csproj	Upgraded to xUnit v3 packages and Microsoft Testing Platform with multi-targeting
build/common.props	Updated target frameworks, enabled nullable/implicit usings, dynamic copyright year, upgraded build packages
global.json	Added test runner configuration for Microsoft Testing Platform
README.md	Enhanced with comprehensive usage examples for all API methods
AGENTS.md	New agent guidelines document with coding standards and repository conventions
.github/workflows/codeql-analysis.yml	New CodeQL analysis workflow
.github/workflows/copilot-setup-steps.yml	New Copilot setup workflow
.github/workflows/build.yml	Added new-test-runner flag for Microsoft Testing Platform

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