Change Unit.multiplier type from decimal to float

Remove remnants related to BigDecimal.

app/helpers/application_helper.rb

@@ -103,15 +103,19 @@ module ApplicationHelper
     def number_field(method, options = {})
       attr_type = object.type_for_attribute(method)
       case attr_type.type
-      when :decimal
+      when :float, :double
         options[:value] = object.public_send(method)&.to_scientific
-        options[:step] ||= BigDecimal(10).power(-attr_type.scale)
-        options[:max] ||= BigDecimal(10).power(attr_type.precision - attr_type.scale) -
-          options[:step]
-        options[:min] = options[:min] == :step ? options[:step] : options[:min]
-        options[:min] ||= -options[:max]
-        options[:size] ||= attr_type.precision / 2
-      when :float
+        options[:step] ||= :any
+        options[:min] ||= Float::MIN_15
+        options[:max] ||= Float::MAX_15
+        # Longest possible number (written not using exponent):
+        #   sign (1), leading 0 (1), dot (1), exponent 0s (307), digits (15).
+        # This is only upper bound, which cannot guarantee the number won't fall
+        # out of range.
+        # TODO: add `[pattern]` to limit precision and (possibly) replace `[maxlength]`?
+        # NOTE: `[pattern]` is unavailable on `input[type=number]` and `[min]/[max]` is
+        # unavailable on `input[type=text]`.
+        options[:maxlength] ||= 3 + Float::MIN_10_EXP + Float::DIG
         options[:size] ||= 6
       end
       super