fix(transit): seq/instanceID heartbeat checks (Node.js parity)

[explosivebit]

Summary

Implements seq/instanceID checks in heartbeat handler matching Node.js Moleculer heartbeatReceived():

• seq mismatch → services changed on remote node → trigger re-discovery
• instanceID mismatch → node restarted → trigger re-discovery
• heartbeat payload now includes seq and instanceID fields

Without this, a remote node that restarts or changes services is never re-discovered via heartbeat — only via the slower INFO round-trip.

Evidence

Step	Result
ruff + mypy	✅ 0 errors
pytest	✅ 2358 passed
demo_matrix	✅ 28/28
demo_comprehensive	✅ 90/90

Test plan

• test_heartbeat_seq_mismatch_triggers_discover
• test_heartbeat_instanceid_mismatch_triggers_discover
• test_heartbeat_same_seq_instanceid_updates_metrics

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
moleculerpy/transit.py	93.33%	0 Missing and 1 partial ⚠️

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