fix: reset regex lastIndex in pattern() to prevent stateful behavior

[Yanhu007]

Fixes #1190

Problem

When a RegExp with the global (/g) or sticky (/y) flag is passed to pattern(), JavaScript's RegExp.prototype.test() mutates lastIndex after each call, causing alternating results on identical inputs:

const Query = pattern(string(), /^example/g)

is({ url: "example" }, Query) // true
is({ url: "example" }, Query) // false (!)
is({ url: "example" }, Query) // true

This is a well-known JavaScript gotcha.

Fix

Reset lastIndex to 0 before each test() call in the pattern refinement. This ensures consistent results regardless of regex flags.