DSH-RSS: RSS/Atom Feed Tool Plugin for DSH

dsh-rss is an RSS/Atom subscription tool plugin within the DSH ecosystem, designed to streamline the process by which models obtain external information. This plugin encapsulates crawling, parsing, and subscription management into standardized tools, addressing the complex and inconsistent issues associated with manual handling of HTTP requests, XML parsing, and date formatting. Core features include: subscription CRUD operations (`rss_list`, `rss_add`, etc.), entry fetching and parsing (`rss_fetch`), cross-source keyword search (`rss_search`), and OPML format import/export. The plugin provides output normalization capabilities, such as converting dates to ISO 8601, transforming relative links to absolute links, and text cleaning. Additionally, it enforces security boundaries, limiting response size to 5MB and not parsing DTD/external entities. Subscription lists are persistently stored in setti