RUST-BUG-111: run ED2K connected startup only on a new client ID

[itlezy]

What

Stock eMule performs the connected-server transition exactly once per assigned client ID. OP_IDCHANGE previously re-ran the full startup path on every packet, re-emitting \ConnectSucceeded\ and republishing the offer-file catalog when a server echoed IDCHANGE or re-sent it after the callback test.

This change gates the \ConnectSucceeded\ event and \send_connected_server_startup\ on:

• first accepted login, or
• a real client-ID reassignment (e.g. LowID-to-HighID).

Server flags and public-IP state are still refreshed on every non-zero IDCHANGE, matching stock behavior.

Tests

• 
  edundant_same_id_idchange_does_not_rerun_connected_startup\
• \client_id_reassignment_reruns_connected_startup\

Both exercise \handle_server_packet\ with a real connected session and assert ConnectSucceeded counts plus public-IP/assigned-ID state.

Validation

• \cargo test -p emulebb-ed2k\ (1026 passed)
• \python tools/rust_quality_gate.py quick\ (policy, rustfmt, clippy, diagnostics binary, WebUI)

Closes #76