Replace /// <reference types="node" /> with explicit import type in typings

[deyaaeldeen]

Remove the triple-slash directive /// <reference types="node" /> from all 16 typing files in typings/. This directive injects the entire @types/node global namespace into any TypeScript project that imports rhea, even when compiling for non-Node targets (React Native, browser, Cloudflare Workers), causing type conflicts.

What changed

• Removed /// <reference types="node" /> from all 16 .d.ts files
• Added import type { Buffer } from "buffer" to the 9 files that use Buffer without an explicit import (connection.d.ts, frames.d.ts, link.d.ts, message.d.ts, sasl.d.ts, session.d.ts, transport.d.ts, types.d.ts, util.d.ts)
• Files that already had explicit import { ... } from "events" / import { ... } from "net" needed no additional changes

Why

The /// <reference types="node" /> is a legacy pattern from before import type existed. It pulls in all Node.js type definitions globally, which conflicts with other platform type definitions (e.g., react-native, lib.dom.d.ts) that define the same globals (FormData, AbortController, Blob, etc.).

Using explicit import type resolves identically for Node consumers (since @types/node provides the "buffer", "events", and "net" modules) but avoids polluting consumers' global type namespace.

Validation

• tsc --noEmit passes with zero errors
• Non-breaking change: all types resolve identically for Node consumers

Fixes #446