Fastify Integration for Better Auth

Fastify Better Auth is a Fastify plugin designed to seamlessly integrate the `better-auth` authentication library into Fastify applications. It automates the registration of all necessary authentication routes, typically under `/api/auth/*`, and decorates the Fastify instance with utilities to access the `better-auth` instance and manage session data. The current stable version is 1.2.0, with minor feature releases indicating active development. Key differentiators include its focus on type-safe decorator access to the auth instance via `getAuthDecorator()` and its direct compatibility with Fastify 5.x and Better Auth 1.x, simplifying setup for applications using these specific versions.