Add Alanube MCP support

[wilmerm]

Goal: Integrate a client for the newly released Alanube MCP server, which exposes 30 e-invoicing tools for AI agents via JSON-RPC.

Key tasks:

1. Create AlanubeMCPClient: a class handling connection to the MCP endpoint (https://sandbox-mcp.alanube.co/mcp/rd) and token-based authentication.
2. Map tools to Python methods across the three catalog layers:
   • Orchestration (priority): issue_and_track_rd_document
   • Issuance/Status: 10 pairs for each e-CF type (31–47)
   • Diagnostics: diagnose_rd_api_error, validate_rd_request_payload
3. Support key flows: synchronous (immediate response) and asynchronous (configurable polling via max_status_checks and status_check_interval_ms).
4. Tests and examples against the sandbox, including the documented quick start.

Expected outcome: issue and track e-invoices from Python with a clean API like:

client = AlanubeMCPClient(api_token="...")
result = client.issue_and_track_document(
    document_type_code="32",
    payload={...},
    wait_for_final_status=True
)