Check if a Number Is Prime / Integer Square Root

Question

## Problem

Write the most efficient routine to test primality and to compute integer square root without floating point.

## Example
```
isPrime(97) -> true; isqrt(50) -> 7
```

## Constraints
- n up to 10^12

## Approach
Trial division up to √n for primality; binary search or Newton's method for isqrt. Discuss overflow.