Fix: #3342 hexadecimal input not turned into a bigint

[josdejong]

Fixes #3342 (comment)

[gwhitney]

The following definition of safeNumberType passes all tests:

export function safeNumberType (numberStr, config) {
  if (config.number === 'bigint') {
    try {
      BigInt(numberStr)
    } catch {
      return config.numberFallback
    }
  }

  return config.number
}

If we adopted this, we would not need the three new "isXXXStr" functions, and we would be future-proofing mathjs against any other integer notations. Would you like to switch to this? If so, will you do the refactoring or would you like me to? Just let me know.