fix(csv-stringify): preserve negative numeric values

[lux-liang]

Summary

• preserve negative number and bigint fields when escape_formulas is enabled
• continue escaping string fields that begin with -
• add regression coverage for both numeric and string inputs

Fixes #503

Testing

• npm --workspace csv-stringify test (212 passing, 1 pending)
• npx eslint lib/api/index.js test/option.escape_formulas.ts