Caches of outside APIs live in /var/cache/sww (closes #314)

The answers of GeoJS, the lists fetched by URL, the DNS blocklists,
AbuseIPDB and routewatch each go in a cache file in SWW_CACHE_DIR
(default /var/cache/sww): lookups.json, lists.json, dnsbl.json,
abuseipdb-scores.json and routewatch.json. reputation.json is gone. The
AbuseIPDB checks spent today are a count, not a cache, and stay in
SWW_STATE_DIR as abuseipdb-checks-spent.json.

A cache file never stops the start: one that does not parse is set
aside as an edit is, one that cannot be read is written over, and its
cache starts empty. An unwritable SWW_CACHE_DIR stops the start, as an
unwritable SWW_STATE_DIR does. Each directory is watched on its own.
The run script makes the cache directory and gives it to sww.

Model: opus-5-5

internal/metrics/metrics.go

@@ -120,17 +120,19 @@ func New(topN int, instanceName string) *Metrics {
 				"went on without it, because GeoJS had not given it in time.",
 		}),
 		stateFileWrites: counterVec("sww_state_file_writes_total",
-			"Writes of each state file.", byFile),
+			"Writes of each state or cache file.", byFile),
 		stateFileWriteFailures: counterVec("sww_state_file_write_failures_total",
-			"Writes of each state file that failed.", byFile),
+			"Writes of each state or cache file that failed.", byFile),
 		stateFileLastWrite: gaugeVec("sww_state_file_last_write_timestamp_seconds",
-			"When each state file was last written, in seconds since 1970.", byFile),
+			"When each state or cache file was last written, in seconds since 1970.",
+			byFile),
 		stateFileSize: gaugeVec("sww_state_file_size_bytes",
-			"The size of each state file, as it was last written.", byFile),
+			"The size of each state or cache file, as it was last written.", byFile),
 		stateFileEditsTakenIn: counterVec("sww_state_file_edits_taken_in_total",
-			"Edits of each state file taken in while running.", byFile),
+			"Edits of each state or cache file taken in while running.", byFile),
 		stateFileEditsSetAside: counterVec("sww_state_file_edits_set_aside_total",
-			"Edits of each state file renamed to <name>.bad because they did not parse.",
+			"Edits of each state or cache file renamed to <name>.bad because they "+
+				"did not parse.",
 			byFile),
 	}
 
@@ -447,8 +449,8 @@ func (m *Metrics) CoreRuleSetMatched(mode string, id int) {
 	m.coreRuleSetMatches.WithLabelValues(mode, strconv.Itoa(id)).Inc()
 }
 
-// StateFileWritten counts a write of the state file name, of size bytes,
-// that ended with err.
+// StateFileWritten counts a write of the state or cache file name, of size
+// bytes, that ended with err.
 func (m *Metrics) StateFileWritten(name string, size int, err error) {
 	m.stateFileWrites.WithLabelValues(name).Inc()
 
@@ -466,13 +468,13 @@ func (m *Metrics) StateFileWritten(name string, size int, err error) {
 	m.stateFileSize.WithLabelValues(name).Set(float64(size))
 }
 
-// StateFileEditTakenIn counts an admin's edit of the state file name
+// StateFileEditTakenIn counts an admin's edit of the state or cache file name
 // taken in while sww runs.
 func (m *Metrics) StateFileEditTakenIn(name string) {
 	m.stateFileEditsTakenIn.WithLabelValues(name).Inc()
 }
 
-// StateFileEditSetAside counts an admin's edit of the state file name
+// StateFileEditSetAside counts an admin's edit of the state or cache file name
 // renamed to name.bad because it did not parse.
 func (m *Metrics) StateFileEditSetAside(name string) {
 	m.stateFileEditsSetAside.WithLabelValues(name).Inc()