Function loopUnroll

loopUnroll($loop: DoStatement, factor: number): DoStatement[]
Unrolls a range do-loop by the given factor.

Two loops replace the original:
- A main loop that steps by factor, with the body replicated factor times (each copy substitutes var with var+offset for offset 0..factor-1).
- A cleanup loop that handles the remaining < factor iterations with the original body. When factor exactly divides the trip count, the cleanup loop's bounds produce a no-op and it generates no iterations.
If the loop is not a range loop, has an explicit non-unit step, or factor is ≤ 1, the loop is left unchanged and returned as a single-element array.
Parameters
- $loop: DoStatement
  The do-loop to unroll.
- factor: number
  The unroll factor (must be ≥ 2).
Returns DoStatement[]
The replacement loops inserted into the AST, in source order.
Example
```
// Before (factor = 4):
// do i = 1, n
//   a(i) = b(i)
// end do

// After:
// do i = 1, (n) - 3, 4
//   a(i) = b(i); a(i+1) = b(i+1); a(i+2) = b(i+2); a(i+3) = b(i+3)
// end do
// do i = (1) + (((n) - (1) + 1) / 4) * 4, n
//   a(i) = b(i)
// end do
```
- Defined in metafor/Fortran-JS/src-api/code/LoopUnroll.ts:51