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/doc.go

@@ -0,0 +1,28 @@
+/*
+Package asinfo provides information about Autonomous Systems (AS).
+
+The package embeds a comprehensive database of AS numbers, handles, and descriptions
+sourced from https://github.com/ipverse/asn-info. The data is embedded at compile
+time and provides fast, offline lookups.
+
+Basic usage:
+
+	// Get information about an AS
+	info, ok := asinfo.Get(15169)
+	if ok {
+		fmt.Printf("AS%d: %s - %s\n", info.ASN, info.Handle, info.Description)
+	}
+
+	// Get just the description
+	desc := asinfo.GetDescription(15169) // "Google LLC"
+
+	// Search for AS entries
+	results := asinfo.Search("University")
+	for _, as := range results {
+		fmt.Printf("AS%d: %s\n", as.ASN, as.Description)
+	}
+
+The data is loaded lazily on first access and cached in memory for the lifetime
+of the program. All getter methods are safe for concurrent use.
+*/
+package asinfo