Introduce TimeProvider for testable time-dependent behavior

[Copilot]

• Add Microsoft.Bcl.TimeProvider package reference to MiniJwt.Core.csproj for .NET 6 and 7
• Add private readonly TimeProvider field to MiniJwtService
• Create new constructor accepting TimeProvider parameter (primary constructor with implementation)
• Modify existing constructor to chain to new constructor with TimeProvider.System
• Replace DateTime.UtcNow with _timeProvider.GetUtcNow().UtcDateTime on line 112
• Add Microsoft.Extensions.TimeProvider.Testing package to test project
• Update tests to use FakeTimeProvider for time-sensitive tests
• Update documentation (README.md) to mention TimeProvider support for testing
• Update examples.md with TimeProvider testing examples using correct API
• Update faq.md to reference TimeProvider testing
• Build and test all changes

Original prompt

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This section details on the original issue you should resolve

<issue_title>Introduire TimeProvider (standard .NET 8, disponible via package Microsoft.Bcl.TimeProvider pour les vieilles versions).</issue_title>
<issue_description>Ajouter un constructeur qui accepte TimeProvider, et garder l'ancien constructeur qui appelle le nouveau avec TimeProvider.System.

private readonly TimeProvider _timeProvider;

// Constructeur existant (modifié pour chain)
public MiniJwtService(IOptionsMonitor<MiniJwtOptions> optionsMonitor, ILogger<MiniJwtService> logger, JwtSecurityTokenHandler tokenHandler) 
    : this(optionsMonitor, logger, tokenHandler, TimeProvider.System)
{
}

// Nouveau constructeur (optionnel pour l'utilisateur, vital pour tes tests)
public MiniJwtService(IOptionsMonitor<MiniJwtOptions> optionsMonitor, ILogger<MiniJwtService> logger, JwtSecurityTokenHandler tokenHandler, TimeProvider timeProvider)
{
    _timeProvider = timeProvider;
    // ... reste de l'init
}

// Utilisation ligne 394
var now = _timeProvider.GetUtcNow().UtcDateTime;

Appliquer ces modifications dans les tests et dans la documentation</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Introduire TimeProvider (standard .NET 8, disponible via package Microsoft.Bcl.TimeProvider pour les vieilles versions). #20

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[Copilot]

Pull request overview

This PR introduces TimeProvider support to enable deterministic testing of JWT token generation timestamps. The implementation adds a new optional constructor parameter that accepts a TimeProvider, with backward compatibility maintained through constructor chaining that defaults to TimeProvider.System.

Key Changes

• Added TimeProvider field and constructor overload to MiniJwtService for testable time-dependent behavior
• Replaced DateTime.UtcNow with _timeProvider.GetUtcNow().UtcDateTime in token generation
• Added conditional package references for Microsoft.Bcl.TimeProvider (8.0.1) for .NET 6/7 targets and Microsoft.Extensions.TimeProvider.Testing (8.10.0) for tests

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/MiniJwt.Core/Services/MiniJwtService.cs	Adds TimeProvider field, new constructor accepting TimeProvider, and updates token generation to use injected time provider
src/MiniJwt.Core/MiniJwt.Core.csproj	Adds conditional package reference to Microsoft.Bcl.TimeProvider for .NET 6/7 targets
src/MiniJwt.Tests/MiniJwtTests.Service.cs	Adds two new tests demonstrating FakeTimeProvider usage for fixed-time and time-advancement scenarios
src/MiniJwt.Tests/MiniJwt.Tests.csproj	Adds Microsoft.Extensions.TimeProvider.Testing package reference
docs/examples.md	Adds new testing section with FakeTimeProvider usage example
docs/faq.md	Updates testing guidance to mention FakeTimeProvider
README.md	Adds new "Testing with TimeProvider" section with usage example

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