Add asinfo package for AS number information lookups

- Created pkg/asinfo with embedded AS data from ipverse/asn-info
- Provides fast lookups by ASN with GetDescription() and GetHandle()
- Includes Search() functionality for finding AS by name/handle
- Added asinfo-gen tool to fetch and convert CSV data to JSON
- Added 'make asupdate' target to refresh AS data
- Embedded JSON data contains 130k+ AS entries
- Added comprehensive tests and examples

pkg/asinfo/example_test.go

@@ -0,0 +1,29 @@
+package asinfo_test
+
+import (
+	"fmt"
+
+	"git.eeqj.de/sneak/routewatch/pkg/asinfo"
+)
+
+func ExampleGet() {
+	info, ok := asinfo.Get(15169)
+	if ok {
+		fmt.Printf("AS%d: %s - %s\n", info.ASN, info.Handle, info.Description)
+	}
+	// Output: AS15169: GOOGLE - Google LLC
+}
+
+func ExampleGetDescription() {
+	desc := asinfo.GetDescription(13335)
+	fmt.Println(desc)
+	// Output: Cloudflare, Inc.
+}
+
+func ExampleSearch() {
+	results := asinfo.Search("MIT-GATEWAY")
+	for _, info := range results {
+		fmt.Printf("AS%d: %s - %s\n", info.ASN, info.Handle, info.Description)
+	}
+	// Output: AS3: MIT-GATEWAYS - Massachusetts Institute of Technology
+}