fix(isCurrency): match complete currency symbols literally - #2906

Summary

Escape every non-word character in the configured currency symbol, rather than only the first one.

isCurrency currently accepts a different symbol when a later character has a regular-expression meaning. For example:

isCurrency('S/x10.00', { symbol: 'S/.', require_symbol: true }); // true before this change
isCurrency('دxإ10.00', { symbol: 'د.إ', require_symbol: true }); // true before this change

Both should return false, while the corresponding amounts with the exact configured symbols should remain valid. The same issue affects symbols placed after the amount and optional symbols.

This extends the literal-symbol escaping introduced in #1306 by applying the existing replacement globally. No public options or other currency-formatting rules change.

Validation

• Added three regression tests covering required, optional, and trailing symbols, including a non-ASCII symbol.
• Confirmed all three regressions fail before the source fix and pass afterward.
• npm test: all 326 tests pass, including the full build and lint steps, on Node.js 24.19.0.
• Checked valid and invalid symbol matching in the generated Node entry point, individual Node module, browser bundle, and minified browser bundle.

Checklist

• PR contains only related source and regression-test changes.
• README reviewed; the public API and options are unchanged.
• Regression tests added and the complete test suite passed.
• Related implementation reference provided above.