Keep accented letters in AS names (closes #165)

The built-in AS list had no letter outside ASCII, and make asupdate
rejected today's as.csv, which added a country code column.

The generator now checks only the first three header columns and reads
past the rest; the parsing moved into parseCSV. The list is regenerated.
The new source spells some names differently and no longer lists AS 0
or the documentation AS numbers, so the tests that relied on those
entries changed.

A WHOIS answer that is not valid UTF-8 is now decoded as Latin-1, which
RIPE and APNIC send, before it is parsed and stored. LACNIC answers in
UTF-8.

Model: opus-5-5

internal/whois/whois.go

@@ -11,6 +11,9 @@ import (
 	"regexp"
 	"strings"
 	"time"
+	"unicode/utf8"
+
+	"golang.org/x/text/encoding/charmap"
 )
 
 // Timeout constants for WHOIS queries.
@@ -213,8 +216,8 @@ func (c *Client) queryRIR(
 	return answer, nil
 }
 
-// query performs a raw WHOIS query to the specified server. An answer that
-// reaches maxAnswerSize is an error.
+// query performs a raw WHOIS query to the specified server and returns the
+// answer in UTF-8. An answer that reaches maxAnswerSize is an error.
 func (c *Client) query(ctx context.Context, server, query string) (string, error) {
 	conn, err := c.DialContext(ctx, "tcp", server)
 	if err != nil {
@@ -261,7 +264,25 @@ func (c *Client) query(ctx context.Context, server, query string) (string, error
 		return "", fmt.Errorf("read response: %w", errAnswerTooLarge)
 	}
 
-	return sb.String(), nil
+	return toUTF8(sb.String())
+}
+
+// toUTF8 returns a WHOIS answer in UTF-8. An answer that is valid UTF-8 is
+// returned as it is. Any other answer is decoded as Latin-1, which RIPE and
+// APNIC send. LACNIC, ARIN and AFRINIC send UTF-8. RIPE's database working
+// group lists the five here:
+// https://www.ripe.net/ripe/mail/archives/db-wg/2024-May/008075.html
+func toUTF8(answer string) (string, error) {
+	if utf8.ValidString(answer) {
+		return answer, nil
+	}
+
+	decoded, err := charmap.ISO8859_1.NewDecoder().String(answer)
+	if err != nil {
+		return "", fmt.Errorf("decode Latin-1 answer: %w", err)
+	}
+
+	return decoded, nil
 }
 
 // parseIANAReferral extracts the RIR and WHOIS server from an IANA response.