Honor signDisplay in the native number converter

[jasperan]

Summary

Fixes #70 by threading signDisplay through the native number converter runtime and public option types.

Problem

oj.IntlNumberConverter ignored signDisplay: 'always' even though native Intl.NumberFormat displayed the expected + sign for positive and zero values.

Reproduction

Format positive, zero, and negative values with a JET number converter configured with signDisplay: 'always', then compare the output to native Intl.NumberFormat.

Before this patch, JET returned "5" and "0" where native formatting returned "+5" and "+0".

Changes

• carry signDisplay through the resolved converter option shape
• pass signDisplay into the native formatter options
• update the debug, debug_esm, and minified bundles
• expose signDisplay in the public TypeScript option types

Verification

• compared JET formatter output against native Intl.NumberFormat for positive, zero, and negative values
• confirmed package smoke still passes with npm pack --dry-run

Scope / Caveats

• this patch is scoped to signDisplay behavior in the native number converter path
• it does not redesign unrelated converter options or formatting rules