feat(server): measure bandwidth and report it in NetworkCharacteristicsResult - #1471
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The server-side AutoDetectManager measures RTT but never reports the result back to the client, so clients cannot use the measurement to size their receive buffers. Add a NETCHAR_RESULT_RTT emission on the MCS message channel: a netchar_result_rtt() constructor (baseRTT + averageRTT, no bandwidth), an AutoDetectManager::build_netchar_result() that reports the lowest and average observed RTT once samples exist, and a send site on the existing auto-detect tick that reuses the message-channel framing from the RTT request path. Bandwidth is intentionally omitted here; a follow-up adds continuous bandwidth measurement and upgrades the result to NETCHAR_RESULT_ALL. Also corrects a stale doc comment on send_rtt_request that referred to the IO channel Share Data PDU (auto-detect moved to the MCS message channel).
…csResult Builds on the RTT-only Network Characteristics Result: the server now runs a continuous Bandwidth Measure over the MCS message channel and folds the result into the report, so a participating client (mstsc, RDM, FreeRDP) receives the full baseRTT + bandwidth + averageRTT characteristics rather than RTT alone. Once per BW_MEASURE_INTERVAL_TICKS auto-detect ticks the AutoDetectManager emits a Bandwidth Measure transaction (Start -> Payload -> Stop, request type 0x0014 / 0x0429) back-to-back so the client counts only the payload window; its Bandwidth Measure Results reply (timeDelta + byteCount) is turned into a kbps figure that upgrades the emitted result to the all-fields form. A measurement is never started while one is outstanding. Reuses the existing message-channel framing; no new PDU types.
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Stacked on #1470; review and merge that first. This branch's first commit is #1470 and the second is the change here.
Extends the server-side auto-detect added by #1470. The RTT-only Network Characteristics Result becomes the full baseRTT plus bandwidth plus averageRTT report by adding a continuous Bandwidth Measure over the MCS message channel.
Change: once per N auto-detect ticks, AutoDetectManager emits a Bandwidth Measure transaction (Start, Payload, Stop; continuous request type 0x0014 / 0x0429) back to back on the message channel. The client counts the payload window and replies with a Bandwidth Measure Results PDU (timeDelta plus byteCount); the manager turns that into a kbps figure and upgrades the next Network Characteristics Result from the RTT-only form to the all-fields form (NETCHAR_RESULT_ALL). A new measurement is never started while one is outstanding. It reuses the message-channel framing from #1348 and adds no new PDU types.
Testing: unit and integration tests cover pacing, the Start/Payload/Stop transaction sharing one sequence number, bandwidth-results handling, and the RTT-only to all-fields upgrade. All cargo xtask check gates (fmt, lints, tests) pass locally.