Remove the per-peer route tables (closes #122)

The routing table in memory now holds every route, so the two per-peer route
tables go, with every write, delete, count and read that served them. The
prefix handler applies each update to the table, writes the table's changes
every second, and stores each new prefix with its first-seen time. The peer
delete, its retry on the next flush and the updates held for it go too. The
types and errors of the server's answers move to internal/server.

The image's memory settings fit a full table of about 1 GB: GOMEMLIMIT of
2.5 GiB, a 512 MiB page cache for the writing connection, and SQLite heap
limits of 768 MiB and 1 GiB. The README describes the new table, its
database copy and the memory budget.

Model: opus-5-5

internal/database/schema.sql

@@ -89,65 +89,6 @@ CREATE INDEX IF NOT EXISTS idx_bgp_peers_asn ON bgp_peers(peer_asn);
 CREATE INDEX IF NOT EXISTS idx_bgp_peers_last_seen ON bgp_peers(last_seen);
 CREATE INDEX IF NOT EXISTS idx_bgp_peers_ip ON bgp_peers(peer_ip);
 
--- IPv4 routing table maintained by PrefixHandler. A route write changes the
--- table and its entry in every index on a column the write sets, so the table
--- has only the indexes that the queries named with them use.
-CREATE TABLE IF NOT EXISTS live_routes_v4 (
-	-- The row id, which the prefix-length pages' sample draws through the
-	-- mask_length index. Declared as a column, it stays the same for as long
-	-- as the route is live, also through a VACUUM.
-	id INTEGER PRIMARY KEY,
-	prefix TEXT NOT NULL,
-	mask_length INTEGER NOT NULL, -- CIDR mask length (0-32)
-	origin_asn INTEGER NOT NULL,
-	peer_ip TEXT NOT NULL,
-	as_path TEXT NOT NULL, -- JSON array
-	next_hop TEXT NOT NULL,
-	last_updated DATETIME NOT NULL,
-	-- A peer has at most one route for a prefix. This key finds the route a
-	-- write updates or deletes and, peer_ip coming first, all of a peer's
-	-- routes when its BGP session goes down.
-	UNIQUE(peer_ip, prefix)
-);
-
--- IPv6 routing table maintained by PrefixHandler, as live_routes_v4.
-CREATE TABLE IF NOT EXISTS live_routes_v6 (
-	id INTEGER PRIMARY KEY,
-	prefix TEXT NOT NULL,
-	mask_length INTEGER NOT NULL, -- CIDR mask length (0-128)
-	origin_asn INTEGER NOT NULL,
-	peer_ip TEXT NOT NULL,
-	as_path TEXT NOT NULL, -- JSON array
-	next_hop TEXT NOT NULL,
-	last_updated DATETIME NOT NULL,
-	UNIQUE(peer_ip, prefix)
-);
-
--- Indexes for both live route tables, and the queries that use each.
---
--- prefix, last_updated: a prefix's routes, for the prefix page and its API
--- answer, the IP lookup and its peer count, and the check whether a prefix
--- still has a live route; and a prefix's newest route for the prefix-length
--- pages and the AS page, in one search whatever the number of peers.
-CREATE INDEX IF NOT EXISTS idx_live_routes_v4_prefix_last_updated ON live_routes_v4(prefix, last_updated);
-CREATE INDEX IF NOT EXISTS idx_live_routes_v6_prefix_last_updated ON live_routes_v6(prefix, last_updated);
--- mask_length: the prefix-length pages' random sample, the row id range of a
--- mask length and the first route of it at or after a row id.
-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_v6_mask_length ON live_routes_v6(mask_length);
--- mask_length, prefix: the prefix-length pages' list of a mask length's
--- prefixes in text order, and the prefix distribution read at startup.
-CREATE INDEX IF NOT EXISTS idx_live_routes_v4_mask_prefix ON live_routes_v4(mask_length, prefix);
-CREATE INDEX IF NOT EXISTS idx_live_routes_v6_mask_prefix ON live_routes_v6(mask_length, prefix);
--- origin_asn, prefix: the prefixes an AS originates, each in one search
--- whatever the number of peers, for the AS page and its API answer.
-CREATE INDEX IF NOT EXISTS idx_live_routes_v4_origin_prefix ON live_routes_v4(origin_asn, prefix);
-CREATE INDEX IF NOT EXISTS idx_live_routes_v6_origin_prefix ON live_routes_v6(origin_asn, prefix);
--- last_updated: the oldest and newest route times in /api/v1/stats and
--- /status.json.
-CREATE INDEX IF NOT EXISTS idx_live_routes_v4_last_updated ON live_routes_v4(last_updated);
-CREATE INDEX IF NOT EXISTS idx_live_routes_v6_last_updated ON live_routes_v6(last_updated);
-
 -- The whole routing table, as internal/routetable keeps it in memory: one row
 -- for each prefix and origin AS that some peer carries. Startup reads every
 -- row, and the rows of the pairs that change are written back.