Added reverse connect implementation

[Haeavar]

OPC UA Reverse Connect implementation (Part 6 §7.1.3 / Part 2 §6.14) inverts who dials the TCP socket: the server dials out to pre-configured client URIs, immediately sends a ReverseHello message, and the client then drives the rest of the OPC UA session exactly as in a normal connection (OpenSecureChannel → CreateSession → ActivateSession …).

Usage:

from asyncua import Server, ReverseConnectConfig, ReverseConnectClientEntry

server = Server()
await server.init()
server.reverse_connect = ReverseConnectConfig(
    clients=[
        ReverseConnectClientEntry(endpoint_url="opc.tcp://client-host:4840"),
    ],
    connect_interval=15_000,   # retry every 15 s
    connect_timeout=30_000,
    reject_timeout=60_000,
)
async with server:
    await asyncio.sleep(3600)

[oroulet]

docstring after the variable. Is that normal?

[oroulet]

useless comment

[oroulet]

if it is a config then call it a config...

[oroulet]

Can you rebase?