Add CsTomlFileSerializer.Deserialize/DeserializeAsync/Serialize/SerializeAsync overload accepting TomlFileExtensionPolicy

[prozolic]

#102

This PR add CsTomlFileSerializer.Deserialize/DeserializeAsync/Serialize/SerializeAsync overload accepting TomlFileExtensionPolicy.

public partial class CsTomlFileSerializer
{
    public static T Deserialize<T>(string tomlFilePath, CsTomlSerializerOptions? options, TomlFileExtensionPolicy extensionPolicy);
    public static ValueTask<T> DeserializeAsync<T>(string tomlFilePath, CsTomlSerializerOptions? options, TomlFileExtensionPolicy extensionPolicy, bool configureAwait = false, CancellationToken cancellationToken = default);
    public static void Serialize<T>(string tomlFilePath, T value, CsTomlSerializerOptions? options, TomlFileExtensionPolicy extensionPolicy);
    public static ValueTask SerializeAsync<T>(string tomlFilePath, T value, CsTomlSerializerOptions? options, TomlFileExtensionPolicy extensionPolicy, bool configureAwait = false, CancellationToken cancellationToken = default);
}

public enum TomlFileExtensionPolicy
{
    Strict = 0,
    Relaxed = 1
}

[Copilot]

Pull request overview

This PR addresses issue #102 by adding an opt-in mechanism to relax the .toml file-extension requirement in CsTomlFileSerializer through new overloads that accept a TomlFileExtensionPolicy.

Changes:

• Added TomlFileExtensionPolicy enum (Strict / Relaxed) in CsToml.Extensions.
• Added Deserialize / DeserializeAsync / Serialize / SerializeAsync overloads that accept TomlFileExtensionPolicy, with the existing overloads forwarding to Strict.
• Added test coverage validating strict vs relaxed behavior across sync/async and serialize/deserialize paths.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
tests/CsToml.Tests/CsTomlFileSerializerExtensionPolicyTest.cs	Adds unit tests covering strict vs relaxed extension behavior across sync/async APIs.
src/CsToml.Extensions/TomlFileExtensionPolicy.cs	Introduces the TomlFileExtensionPolicy enum used by new overloads.
src/CsToml.Extensions/CsTomlFileSerializer.cs	Adds new overloads and centralizes extension validation logic via ValidateExtension.

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