fix(regex): include the empty string when a zero-min quantifier applies to a number pattern

ark/regex/__tests__/regex.test.ts

@@ -223,6 +223,17 @@ contextualize(() => {
 			attest<Regex<"ac" | `ab${string}c`, {}>>(S)
 		})
 
+		// https://github.com/arktypeio/arktype/issues/1625
+		it("* over a digit class allows the empty string", () => {
+			const S = regex("^(\\d*)$")
+			attest<Regex<"" | `${number}`, { captures: ["" | `${number}`] }>>(S)
+		})
+
+		it("? over a digit class allows the empty string", () => {
+			const S = regex("^(\\d?)$")
+			attest<Regex<"" | `${number}`, { captures: ["" | `${number}`] }>>(S)
+		})
+
 		it("unmatched ?", () => {
 			// @ts-expect-error
 			attest(() => regex("?")).type.errors(writeUnmatchedQuantifierError("?"))

ark/regex/quantify.ts

@@ -98,9 +98,13 @@ type tryFastPath<
 	max extends number | null
 > =
 	max extends 0 ? ""
-	: // repeating string or `${number}` any number of times will not change the type
+	: // repeating string or `${number}` any number of times will not change the
+	// type, but zero repetitions produce "", which `${number}` does not include
 	string extends pattern ? string
-	: `${number}` extends pattern ? `${number}`
+	: `${number}` extends pattern ?
+		min extends 0 ?
+			"" | `${number}`
+		:	`${number}`
 	: min extends 0 ?
 		max extends 1 ? "" | pattern
 		: max extends number ? loopFromZero<pattern, max, "", []>