JWT Inspector v2.0.0

This release introduces important improvements, consistency fixes, a move to .NET 9, and a few breaking changes to the library.
The focus is on validation semantics, decoding accuracy, and developer usability.

✨ New Features

• Case-insensitive claim and header handling.
• Improved GetTokenSummary: safer, more readable JSON output.
• DecodePayloadAs<T> and DecodePayloadAsJson now deserialize the raw payload instead of hydrated claims.
• GetSigningAlgorithm returns an empty string ("") if the header is missing.
• ValidateNotBefore(string token, TimeSpan? clockSkew = null) now supports optional clock skew.
• Target framework updated to .NET 9.

⚠️ Breaking Changes

• ValidateNotBefore: signature updated with optional clockSkew parameter.
• GetCustomClaim: now returns object? instead of object.
• ValidateLifetime: validates only temporal claims (exp, nbf), ignoring issuer, audience, and signature.
• ValidateIssuerAndAudience: compares claims directly, without signature validation.
• GetJwtId, GetAudience, GetIssuer: return "" (empty string) when missing instead of null.
• Dropped support for older target frameworks; requires .NET 9.