v2: Refactor translator interfaces for type safety

[mmcdole]

Overview

Refactor translator interfaces to use format-specific types instead of generic interface{}, providing better compile-time guarantees and clearer contracts.

Current State

type Translator interface {
    Translate(feed interface{}, opts *ParseOptions) (*Feed, error)
}

Proposed Design

type AtomTranslator interface {
    Translate(feed *atom.Feed, opts *ParseOptions) (*gofeed.Feed, error)
}

type RSSTranslator interface {
    Translate(feed *rss.Feed, opts *ParseOptions) (*gofeed.Feed, error)
}

type JSONTranslator interface {
    Translate(feed *json.Feed, opts *ParseOptions) (*gofeed.Feed, error)
}

Tasks

• Define format-specific translator interfaces
• Update Parser to use specific translator types
• Update default translators to implement new interfaces
• Remove generic Translator interface
• Update documentation for custom translators

Benefits

• Compile-time type safety - no more interface{} and type assertions
• Clearer API contracts for custom translator implementations
• Better IDE support with proper types
• Eliminates runtime type errors in translators

Migration

Users with custom translators will need to update their implementations to use the specific interfaces rather than the generic one.

Related Issues

• Part of v2 RFC (RFC: gofeed v2 – Proposed Changes #241)