refactor(types)!: remove deprecated FastifyLoggerInstance in favor of FastifyBaseLogger - #6906

Proposal:

• Removes the deprecated FastifyLoggerInstance type from fastify.d.ts and types/logger.d.ts. FastifyLoggerInstance was already marked @deprecated in favor of FastifyBaseLogger, with a TODO noting it should be removed in the next major release. Since this is part of the v6 cleanup, we're removing it now.

Breaking change:

• Yes, anyone importing FastifyLoggerInstance needs to migrate to FastifyBaseLogger, which exposes the same API.

Note:

• To be merged from the “next” branch
• For the next major release of Fastify ( v6 )