Name the setting and value when a size does not parse (closes #429)

A size setting such as chunk_size: banana failed with "invalid size
format: strconv.ParseFloat: parsing "": invalid syntax", naming neither
the setting nor the value. The size decoder now quotes the value, and
Parse checks every size setting after ${...} references are filled in,
so the error reads chunk_size: "banana" is not a size; use a number of
bytes or a unit such as 10MB. This covers chunk_size, blob_size_limit
and s3.part_size, and config set.

Model: opus-5-5

internal/config/keys.go

@@ -129,10 +129,11 @@ func checkKeys(node *yaml.Node, typ reflect.Type, path string,
 	return nil
 }
 
-// checkFilledKeys is checkKeys for data, the config after smartconfig has
-// filled in its ${...} references. A key that a reference brings in is not
-// in the file, and the copy that Encode makes has no line numbers.
-func checkFilledKeys(data map[string]any) error {
+// checkFilledConfig checks data, the config after smartconfig has filled in
+// its ${...} references: its keys with checkKeys, then its size settings
+// with checkSizes. A key that a reference brings in is not in the file, and
+// the copy that Encode makes has no line numbers.
+func checkFilledConfig(data map[string]any) error {
 	var filled yaml.Node
 
 	err := filled.Encode(data)
@@ -140,8 +141,13 @@ func checkFilledKeys(data map[string]any) error {
 		return fmt.Errorf("failed to marshal config data: %w", err)
 	}
 
-	return checkKeys(&filled, reflect.TypeFor[Config](), "",
+	err = checkKeys(&filled, reflect.TypeFor[Config](), "",
 		map[*yaml.Node]bool{}, map[nodeAndType]bool{})
+	if err != nil {
+		return err
+	}
+
+	return checkSizes(&filled, nil)
 }
 
 // checkMappingKeys is checkKeys for a map.