feat: add NATS cache sharing and smart cache refresh

Add two complementary features to reduce remote revision cache staleness:

1. Smart local cache: When current system revision matches cached remote
   revision, force an immediate cache refresh to check for newer revisions.

2. NATS integration: Share cache updates across hosts via NATS pub/sub.
   Hosts publish revision updates when they fetch new data, and subscribe
   to receive updates from other hosts. Features include:
   - Auto-reconnect with infinite retries
   - Graceful fallback when NATS unavailable
   - Filtering by flake URL and hostname

New CLI flags:
  --flake.nats.enable
  --flake.nats.url
  --flake.nats.subject
  --flake.nats.credentials-file

New NixOS module options under services.prometheus.exporters.nixos.flake.nats

Bumps version to 0.3.0.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

go.mod

@@ -1,17 +1,23 @@
 module git.t-juice.club/torjus/nixos-exporter
 
-go 1.23
+go 1.23.0
 
-require github.com/prometheus/client_golang v1.20.5
+require (
+	github.com/nats-io/nats.go v1.48.0
+	github.com/prometheus/client_golang v1.20.5
+)
 
 require (
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
-	github.com/klauspost/compress v1.17.9 // indirect
+	github.com/klauspost/compress v1.18.0 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/nats-io/nkeys v0.4.11 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.55.0 // indirect
 	github.com/prometheus/procfs v0.15.1 // indirect
-	golang.org/x/sys v0.22.0 // indirect
+	golang.org/x/crypto v0.37.0 // indirect
+	golang.org/x/sys v0.32.0 // indirect
 	google.golang.org/protobuf v1.34.2 // indirect
 )