feat: port session 04 — Logging, Signals & Services
- NatsLogger.cs: INatsLogger interface (Noticef/Warnf/Fatalf/Errorf/Debugf/Tracef),
ServerLogging state class with atomic debug/trace flags, rate-limited logging
(RateLimitWarnf/RateLimitDebugf), error variants (Errors/Errorc/Errorsc),
MicrosoftLoggerAdapter bridging to ILogger
- SignalHandler.cs: ProcessSignal (Unix kill via Process), CommandToUnixSignal mapping
(Stop→SIGKILL, Quit→SIGINT, Reopen→SIGUSR1, Reload→SIGHUP), ResolvePids via pgrep,
SetProcessName, Run/IsWindowsService stubs for non-Windows
- 11 tests (6 logger, 5 signal/service)
- WASM/Windows signal stubs already n/a
- All 141 tests pass (140 unit + 1 integration)
- DB: features 368/3673 complete, tests 155/3257 complete (9.6% overall)
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