Read every route from the routing table in memory (part of #122)

The IP lookups, the AS and prefix pages and their API answers, the prefix-length pages and the stats read routes only from the routing table the prefix handler keeps. fx reads the table at startup and gives it to both. AS names, WHOIS details and first-seen times still come from the database.

The IP lookup names the origin AS most peers carry, with the time of the newest kept route. The prefix answers list peers whose routes are not kept without a path or time. The stats gain origins_without_kept_route. They no longer read route times from the per-peer tables, so the two helpers that did are gone.

Model: opus-5-5

internal/database/models.go

@@ -66,7 +66,9 @@ type ASNPeering struct {
 	LastSeen  time.Time
 }
 
-// LiveRoute represents a route in the live routing table
+// LiveRoute represents a route in the live routing table. JSON leaves out an
+// empty AS path, next hop or time: the routing table in memory keeps them only
+// for the two newest routes of each prefix and origin AS.
 //
 //nolint:tagliatelle // field names are the existing JSON API
 type LiveRoute struct {
@@ -75,9 +77,9 @@ type LiveRoute struct {
 	IPVersion   int       `json:"ip_version"`
 	OriginASN   int       `json:"origin_asn"`
 	PeerIP      string    `json:"peer_ip"`
-	ASPath      []int     `json:"as_path"`
-	NextHop     string    `json:"next_hop"`
-	LastUpdated time.Time `json:"last_updated"`
+	ASPath      []int     `json:"as_path,omitempty"`
+	NextHop     string    `json:"next_hop,omitempty"`
+	LastUpdated time.Time `json:"last_updated,omitzero"`
 }
 
 // PrefixDistribution represents the distribution of prefixes by mask length
@@ -108,9 +110,10 @@ type IPInfo struct {
 	CountryCode string `json:"country_code,omitempty"`
 	AbuseEmail  string `json:"abuse_email,omitempty"`
 	RIR         string `json:"rir,omitempty"`
-	// Timestamps
+	// Timestamps. LastSeen is zero, and left out of JSON, when the prefix
+	// keeps no route.
 	FirstSeen time.Time `json:"first_seen"`
-	LastSeen  time.Time `json:"last_seen"`
+	LastSeen  time.Time `json:"last_seen,omitzero"`
 	// Indicates if WHOIS data needs refresh (not serialized)
 	NeedsWHOISRefresh bool `json:"-"`
 }