Add everything-server for MCP conformance testing

Implements a comprehensive reference server that exercises all MCP protocol
features for conformance testing. This server validates that the Python SDK
correctly implements the MCP specification by passing all 25 conformance
test scenarios.

Features implemented:
- 11 tools covering all content types (text, image, audio, embedded resources,
  mixed content, logging, progress, error handling, sampling, elicitation)
- 4 resources (static text/binary, templates, subscribable resources)
- 4 prompts with various content types
- Logging support (logging/setLevel)
- Completion support (completion/complete)
- Resource subscriptions (resources/subscribe, resources/unsubscribe)
- Session management with StreamableHTTP transport

Implementation uses FastMCP with proper type safety:
- All URIs wrapped with AnyUrl() for type correctness
- Context properly typed with ServerSession parameter
- Subscribe/unsubscribe handlers use correct AnyUrl parameter and None return
- Completion handler returns Completion objects
- ElicitationResult uses discriminated union narrowing via action field
- Relative imports in __main__.py to avoid type stub warnings

Type checking: Passes pyright with 0 errors (only 3 targeted ignores for
accessing _mcp_server private API, documented with TODO to add public APIs
to FastMCP in the future).

Conformance: Passes all 25 test scenarios.

Author: felixweinberger

examples/servers/everything-server/README.md

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+# MCP Everything Server
+
+A comprehensive MCP server implementing all protocol features for conformance testing.
+
+## Overview
+
+The Everything Server is a reference implementation that demonstrates all features of the Model Context Protocol (MCP). It is designed to be used with the [MCP Conformance Test Framework](https://github.com/modelcontextprotocol/conformance) to validate MCP client and server implementations.
+
+## Installation
+
+From the python-sdk root directory:
+
+```bash
+uv sync --frozen
+```
+
+## Usage
+
+### Running the Server
+
+Start the server with default settings (port 3001):
+
+```bash
+uv run -m mcp_everything_server
+```
+
+Or with custom options:
+
+```bash
+uv run -m mcp_everything_server --port 3001 --log-level DEBUG
+```
+
+The server will be available at: `http://localhost:3001/mcp`
+
+### Command-Line Options
+
+- `--port` - Port to listen on (default: 3001)
+- `--log-level` - Logging level: DEBUG, INFO, WARNING, ERROR, CRITICAL (default: INFO)
+
+## Running Conformance Tests
+
+See the [MCP Conformance Test Framework](https://github.com/modelcontextprotocol/conformance) for instructions on running conformance tests against this server.

examples/servers/everything-server/mcp_everything_server/__init__.py

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+"""MCP Everything Server - Comprehensive conformance test server."""
+
+__version__ = "0.1.0"

examples/servers/everything-server/mcp_everything_server/__main__.py

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+"""CLI entry point for the MCP Everything Server."""
+
+from .server import main
+
+if __name__ == "__main__":
+    main()