Make live route writes cheaper so the prefix handler keeps up (closes #96)

The live route tables lose their random UUID key: the row id, which the
prefix-length sample draws, is now declared as the integer key. The prefix
tables are keyed by the prefix, without the UUID or the duplicate index.
A route update sets only the columns that change, so SQLite no longer
rewrites the mask length indexes on every update, nor the origin index
while the origin AS stays the same. Each kept index names the queries
that use it. BenchmarkPrefixBatchOnFiveMillionRoutes, run by hand, times
one 25,000-update batch on 5 million routes.

Model: opus-5-5

internal/database/counts_internal_test.go

@@ -29,7 +29,6 @@ func mkV4Route(t *testing.T, prefix string, asn int, ts time.Time) *LiveRoute {
 	}
 
 	return &LiveRoute{
-		ID:          uuid.New(),
 		Prefix:      prefix,
 		MaskLength:  maskLength,
 		IPVersion:   ipVersionV4,
@@ -44,7 +43,6 @@ func mkV4Route(t *testing.T, prefix string, asn int, ts time.Time) *LiveRoute {
 // mkV6Route builds an IPv6 live route.
 func mkV6Route(prefix string, asn int, ts time.Time) *LiveRoute {
 	return &LiveRoute{
-		ID:          uuid.New(),
 		Prefix:      prefix,
 		MaskLength:  32,
 		IPVersion:   ipVersionV6,