feat: structured logging

[lachlanharrisdev]

Solves #12

[Copilot]

Pull request overview

Introduces structured logging across GoNetSim using log/slog, with configurable log format/level and per-service logger injection to improve observability and log consistency.

Changes:

• Add internal/observability.NewLogger (tint text output or JSON) and wire it into CLI commands.
• Inject per-service *slog.Logger via a new optional service.LoggerAware interface and update HTTP/DNS services to use it.
• Add logging configuration defaults and TOML config keys ([logging] format/level), plus small TTY-aware banner formatting.

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
main.go	TTY-aware banner formatting and new color/TTY deps.
cmd/root.go	Create/configure default slog logger from config; structured startup/error logging.
cmd/dns.go	Configure slog logger for standalone DNS command.
cmd/http.go	Configure slog logger for standalone HTTP command.
cmd/https.go	Configure slog logger for standalone HTTPS command.
internal/observability/logging.go	New logger factory supporting text (tint) and JSON output.
internal/config/config.go	Add logging config to schema, defaults, and validation.
internal/config/default_config.toml	Add default [logging] section.
internal/service/service.go	Add LoggerAware interface for logger injection.
internal/service/manager.go	Switch manager to slog, add prefix handler, inject loggers into services.
internal/httpserver/config.go	Store injected logger on HTTP server service.
internal/httpserver/server.go	Pass logger into handler/server and use slog for listening logs.
internal/httpserver/fakemode.go	Structured request logging with captured status code.
internal/httpserver/http_test.go	Update server constructor calls for new logger parameter.
internal/dnsserver/config.go	Store injected logger on DNS server service.
internal/dnsserver/server.go	Add logger-aware server creation and structured query/listen logging.
go.mod	Add tint/colorable/isatty deps; bump x/sys.
go.sum	Add checksums for new deps / updated x/sys.

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