fix: harden SV pacing estimator and isolate unrelated traffic

[masarray]

Summary

Follow-up to PR #49 addressing both review findings before the transport is treated as complete.

Stable interval acquisition

• does not activate pacing from a single observed interval;
• requires four mutually consistent intervals before a nominal SV interval becomes active;
• resets the candidate when observations disagree;
• ignores long scheduler stalls and large deviations after pacing is active;
• adds deterministic tests proving a late first interval cannot permanently reduce the wire rate.

Independent traffic paths

• moves pacing waits to a per-SV-stream semaphore;
• limits the shared Npcap injection semaphore to the short SendPacket critical section;
• allows PTP, GOOSE and other non-SV traffic to pass while an SV stream is waiting for its deadline;
• keeps independent pacing state for every source/destination/APPID/VLAN stream identity.

Tests

Adds coverage for:

• late first-interval rejection;
• inconsistent candidate rejection;
• long scheduler-stall rejection after activation;
• conservative tracking of nearby steady intervals.

Frame encoding, smpCnt, quality, timestamps, VLAN, APPID and capture behavior remain unchanged.

[masarray]

Final validation and review-follow-up evidence:

• Public-source/provenance/license verification passed.
• Windows Release solution build succeeded with 0 warnings and 0 errors.
• AR.Iec61850.Tests: 442/442 passed, including four new pacing-estimator tests.
• A single scheduler-late interval no longer activates pacing; four mutually consistent intervals are required.
• Long stalls and large deviations cannot drag an active nominal rate away from its steady interval.
• SV pacing waits are protected by a per-stream semaphore.
• The shared Npcap injection semaphore is now held only around SendPacket, so PTP, GOOSE and unrelated SV streams are not blocked while one SV stream waits for its deadline.
• Test diagnostic artifact uploaded successfully.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Stop moderate lateness from ratcheting the SV interval

When pacing is active and one send is moderately late—for example, 300 ticks against a 250-tick nominal—this branch accepts the observation and raises the nominal to 255. Because PaceSampledValuesAsync subsequently enforces at least that new nominal between commits, normal 250-tick caller traffic cannot produce a shorter observation to restore the rate; recurring scheduler or injection delays below the 1.5× cutoff can therefore ratchet an SV stream progressively slower. Require consistent independent evidence before updating an active nominal rather than feeding individual paced intervals back into it.

AGENTS.md reference: AGENTS.md:L173-L178

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