Look up IP addresses by prefix at each mask length (closes #48)

Looking up an address read every IPv6 live route and, for IPv4, about
half of the range index. Both families now look the address's prefix up
at each mask length, longest first, on the prefix index: at most 33 or
129 indexed lookups, however many routes are live.

The feed sends IPv6 withdrawals uncompressed but announcements
compressed, so the prefix handler now stores every prefix in the text
form net/netip prints, the form the lookup builds. IPv6 withdrawals now
remove their routes.

The IPv4 range columns, their index and the code that fills them are
removed, and so are the unused GetASInfoForIP lookups.

Model: opus-5-5

internal/database/schema.sql

@@ -107,9 +107,6 @@ CREATE TABLE IF NOT EXISTS live_routes_v4 (
 	as_path TEXT NOT NULL, -- JSON array
 	next_hop TEXT NOT NULL,
 	last_updated DATETIME NOT NULL,
-	-- IPv4 range columns for fast lookups
-	ip_start INTEGER NOT NULL, -- Start of IPv4 range as 32-bit unsigned int
-	ip_end INTEGER NOT NULL,    -- End of IPv4 range as 32-bit unsigned int
 	UNIQUE(prefix, origin_asn, peer_ip)
 );
 
@@ -123,7 +120,6 @@ CREATE TABLE IF NOT EXISTS live_routes_v6 (
 	as_path TEXT NOT NULL, -- JSON array
 	next_hop TEXT NOT NULL,
 	last_updated DATETIME NOT NULL,
-	-- Note: IPv6 doesn't use integer range columns
 	UNIQUE(prefix, origin_asn, peer_ip)
 );
 
@@ -132,8 +128,6 @@ CREATE INDEX IF NOT EXISTS idx_live_routes_v4_prefix ON live_routes_v4(prefix);
 CREATE INDEX IF NOT EXISTS idx_live_routes_v4_mask_length ON live_routes_v4(mask_length);
 CREATE INDEX IF NOT EXISTS idx_live_routes_v4_origin_asn ON live_routes_v4(origin_asn);
 CREATE INDEX IF NOT EXISTS idx_live_routes_v4_last_updated ON live_routes_v4(last_updated);
--- Indexes for IPv4 range queries
-CREATE INDEX IF NOT EXISTS idx_live_routes_v4_ip_range ON live_routes_v4(ip_start, ip_end);
 -- Index to optimize prefix distribution queries
 CREATE INDEX IF NOT EXISTS idx_live_routes_v4_mask_prefix ON live_routes_v4(mask_length, prefix);