fix: keep the sign before the radix prefix for negative numbers

[spokodev]

Problem

With numbers set to 'hexadecimal', 'binary', or 'octal', a negative number or bigint is serialized to a syntactically invalid JavaScript literal, because Number#toString(radix) / BigInt#toString(radix) place the minus sign before the digits — which leaves it after the radix prefix:

const jsesc = require('jsesc');

jsesc(-42, { numbers: 'hexadecimal' }); // '0x-2A'
jsesc(-42, { numbers: 'binary' });      // '0b-101010'
jsesc(-42, { numbers: 'octal' });       // '0o-52'

eval('(0x-2A)'); // SyntaxError: Invalid or unexpected token

The output therefore can't be evaluated or parsed, which contradicts jsesc's contract of producing valid JavaScript. The decimal branch already produces a valid signed literal (jsesc(-42) → '-42'), so this is an inconsistency in the other radixes. bigints are affected identically (-42n → '0x-2An').

Fix

Hoist the sign so it precedes the radix prefix, producing a valid signed literal (-0x2A). Works for both numbers and bigints.

Test

Added assertions that negative hexadecimal / binary / octal output keeps the sign before the prefix. The existing numbers vector that includes a negative bigint had baked in the invalid 0x-… / 0b-… / 0o-… output; those expectations are updated to the corrected -0x… / -0b… / -0o… literals. The full suite is green.