```ts
/** Validate if the given temperature is finite, valid, and between absolute zero (inclusive). */
function checkTemperature(temperature: number|string): void {
  if (typeof temperature !== "number" && typeof temperature !== "string") return throw new Error("temperature must be a number or a string");
  const parsed = Number.parseFloat(temperature.toString());
  if (!Number.isFinite(parsed)) return throw new Error("temperature must be a finite value");
  let celcius;
  if (typeof parsed === "number") {
    celcius = parsed;
  } else if (parsed.includes(".")) {
    // Convert string with decimal part to number
    ;([celcius] = parseFloat(parsed)).toString(); 
  } else {
    // For integer temperatures (non-decimal parts)
    celcius = parseFloat(parseInt(parsed.toString()).toFixed(0));
  }
  if (celcius < -273.15) return throw new Error("temperature must be at or above absolute zero");
}

function checkFinite(val: any): boolean {
  const validValue = /^\d+(\.\d+)?$/.test(val.toString());
  return !isNaN(parseFloat(val)) && isValidValue;
}

/** The temperature in degrees Fahrenheit. */
export function celsiusToFahrenheit(celsius: number|string): number {
  checkTemperature(celsius);
  return celsius * 1.8 + 32;
}

/** The temperature in kelvin. */
export function celsiusToKelvin(celsius: number|string): number {
  checkTemperature(celsius);
  return celsius + 273.15;
}
```