Enforce Go style rules across codebase

Apply five style rules: convert iota string enums to typed
string constants, replace errors.As with errors.AsType,
merge three-group imports into two groups, fix multiline
parameter/argument formatting, and replace fmt.Sprintf URL
construction with net/url.

Signed-off-by: Émile Ré <emile@probo.com>

pkg/coredata/email.go

@@ -176,20 +176,23 @@ func (emails Emails) BulkInsert(
 
 	rows := make([][]any, 0, len(emails))
 	for _, e := range emails {
-		rows = append(rows, []any{
-			e.ID,
-			e.RecipientEmail,
-			e.RecipientName,
-			e.SenderName,
-			e.ReplyTo,
-			e.UnsubscribeURL,
-			e.MailingListUpdateID,
-			e.Subject,
-			e.TextBody,
-			e.HtmlBody,
-			e.CreatedAt,
-			e.UpdatedAt,
-		})
+		rows = append(
+			rows,
+			[]any{
+				e.ID,
+				e.RecipientEmail,
+				e.RecipientName,
+				e.SenderName,
+				e.ReplyTo,
+				e.UnsubscribeURL,
+				e.MailingListUpdateID,
+				e.Subject,
+				e.TextBody,
+				e.HtmlBody,
+				e.CreatedAt,
+				e.UpdatedAt,
+			},
+		)
 	}
 
 	_, err := conn.CopyFrom(