feat: add TypeScript definitions and paginated room message history

[NandanPaT-eL]

Summary

• add src/index.d.ts so TypeScript users get types for the public API
• add in-memory room message storage with getRoomMessages(roomId, page, limit)
• return paginated room message history and clear it on closeRoom()
• restore validation tests and align test expectations with current auth error messages
• document TypeScript support, pagination behavior, and single-process limitation in the README

Details

• sendMessage() now stores messages in memory per room
• getRoomMessages() returns paginated results, where page 1 is the most recent messages
• pagination is capped to a reasonable page size and room history is capped in memory to avoid unbounded growth
• editMessage() now warns if the target message is not present in the in-memory store
• package metadata now points to src/index.d.ts via the types field

Why

This improves developer experience for TypeScript consumers and adds a practical way to load older chat messages without fetching the full room history at once.

Notes

• room message pagination currently uses in-memory storage, so it is intended for single-process deployments
• verified with npm test (34 passed, 0 failed)