Adopt C# 12 syntax across library and tests for .NET 8

[Copilot]

This updates the codebase to use the latest C# language features available with .NET 8. The change standardizes language configuration and applies targeted C# 12 syntax upgrades without altering runtime behavior.

• Language version alignment

  • Set library project language version explicitly to 12.0 (the latest C# level for .NET 8) instead of floating latest.

• Core library modernization

  • Replaced legacy empty array initialization with C# 12 collection expressions.
  • Replaced verbose constructor typing with target-typed new(...) where the type is already known.
  • Simplified temporary array construction in dynamic meta-object binding logic using typed collection expressions.

• Test data modernization

  • Converted test record arrays to collection expressions.
  • Switched dictionary test fixtures to indexer initializers for clearer key/value construction.

Example of the applied style update:

private static readonly string[] s_emptyArray = [];
Expression[] parameters = [Expression.Constant(binder.Name), value.Expression];

public static readonly IReadOnlyList<object> CsvAnonymousRecords =
[
    new { Id = 1, Name = "kazuakix", Location = "Wakayama" },
    new { Id = 2, Name = "daruyanagi", Location = "Ehime" },
    new { Id = 3, Name = "buchizo", Location = "Osaka" }
];

[Copilot]

Pull request overview

Updates the solution to consistently use C# 12 features on .NET 8, modernizing several initialization patterns in the core library and test fixtures.

Changes:

• Pin the library project’s C# language version to 12.0.
• Modernize core library code using C# 12 collection expressions and target-typed new.
• Update test data fixtures to use collection expressions and dictionary indexer initializers.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
CsvHelper.FastDynamic/CsvRecordMetaObject.cs	Replace legacy array initializations with C# 12 collection expressions in DLR binding.
CsvHelper.FastDynamic/CsvReaderExtensions.cs	Use collection expression for empty list initialization in async record collection.
CsvHelper.FastDynamic/CsvHelper.FastDynamic.csproj	Pin C# language version to 12.0.
CsvHelper.FastDynamic/CsvHeader.cs	Use target-typed new for dictionary construction.
CsvHelper.FastDynamic.Tests/TestData.cs	Modernize test fixtures with collection expressions and indexer initializers.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.