Split prefixes table into prefixes_v4 and prefixes_v6

- Create separate tables for IPv4 and IPv6 prefixes in schema.sql
- Update indexes for new prefix tables
- Update getOrCreatePrefix to use appropriate table based on IP version
- Update GetStatsContext to count prefixes from both tables
- Remove ip_version column since it's implicit in the table name

internal/database/schema.sql

@@ -11,10 +11,18 @@ CREATE TABLE IF NOT EXISTS asns (
 	last_seen DATETIME NOT NULL
 );
 
-CREATE TABLE IF NOT EXISTS prefixes (
+-- IPv4 prefixes table
+CREATE TABLE IF NOT EXISTS prefixes_v4 (
+	id TEXT PRIMARY KEY,
+	prefix TEXT UNIQUE NOT NULL,
+	first_seen DATETIME NOT NULL,
+	last_seen DATETIME NOT NULL
+);
+
+-- IPv6 prefixes table
+CREATE TABLE IF NOT EXISTS prefixes_v6 (
 	id TEXT PRIMARY KEY,
 	prefix TEXT UNIQUE NOT NULL,
-	ip_version INTEGER NOT NULL, -- 4 for IPv4, 6 for IPv6
 	first_seen DATETIME NOT NULL,
 	last_seen DATETIME NOT NULL
 );
@@ -52,8 +60,11 @@ CREATE TABLE IF NOT EXISTS bgp_peers (
 	last_message_type TEXT
 );
 
-CREATE INDEX IF NOT EXISTS idx_prefixes_ip_version ON prefixes(ip_version);
-CREATE INDEX IF NOT EXISTS idx_prefixes_version_prefix ON prefixes(ip_version, prefix);
+-- Indexes for prefixes_v4 table
+CREATE INDEX IF NOT EXISTS idx_prefixes_v4_prefix ON prefixes_v4(prefix);
+
+-- Indexes for prefixes_v6 table
+CREATE INDEX IF NOT EXISTS idx_prefixes_v6_prefix ON prefixes_v6(prefix);
 CREATE INDEX IF NOT EXISTS idx_announcements_timestamp ON announcements(timestamp);
 CREATE INDEX IF NOT EXISTS idx_announcements_prefix_id ON announcements(prefix_id);
 CREATE INDEX IF NOT EXISTS idx_announcements_asn_id ON announcements(asn_id);
@@ -61,9 +72,6 @@ CREATE INDEX IF NOT EXISTS idx_peerings_as_a ON peerings(as_a);
 CREATE INDEX IF NOT EXISTS idx_peerings_as_b ON peerings(as_b);
 CREATE INDEX IF NOT EXISTS idx_peerings_lookup ON peerings(as_a, as_b);
 
--- Additional indexes for prefixes table
-CREATE INDEX IF NOT EXISTS idx_prefixes_prefix ON prefixes(prefix);
-
 -- Indexes for asns table
 CREATE INDEX IF NOT EXISTS idx_asns_number ON asns(number);