Look clients up in the IPinfo Lite file with SWWAF_LOOKUP_SOURCE=file (closes #22)

SWWAF_LOOKUP_SOURCE=file looks every client up in the file
SWWAF_LOOKUP_DB_PATH names, without GeoJS. file without the path, the
path with another source, or a file that cannot be read stops the start.
The file is read whole into memory, so overwriting it in place cannot
disturb a lookup, and read again 2 seconds after its last change; a
replacement that cannot be read is logged, counted and sent as a
file_error alert, and the old one stays in use. Metrics give when it
was read and the failed reads. Tests write their databases through
internal/lookup/lookuptest.

Deviation: go.mod and go.sum written by hand; go runs only through make.
Judgement call: the 2-second wait, as the rule files have.

Model: opus-5-5

internal/bans/bans.go

@@ -416,10 +416,10 @@ func (l *Ledger) Bans(netblock netip.Prefix) []Ban {
 }
 
 // AddLookup gives the notes of netblock's bans that have no AS number, AS
-// name or country yet those of a client in it, as GeoJS answered about
-// it. It is not a request from netblock, and leaves when it was last seen
-// unchanged. It does not have bans.json written at once: the notes are
-// written with its next write, as the counts in them are.
+// name or country yet those of a client in it, as the lookup answered
+// about it. It is not a request from netblock, and leaves when it was last
+// seen unchanged. It does not have bans.json written at once: the notes
+// are written with its next write, as the counts in them are.
 func (l *Ledger) AddLookup(netblock netip.Prefix, asn, asName, country string) {
 	l.mu.Lock()
 	defer l.mu.Unlock()