Refactor and Enhance rpow Function in AssemblyBinExp.sol

[SITADRITA1]

Removed duplicate pragma statement

Old:

pragma solidity 0.8.26;
pragma solidity ^0.8.26;

New:

pragma solidity ^0.8.26;

Reason: The second declaration was redundant and unnecessary.
Fixed incorrect handling of 0^n for n > 0

Old:

case 0 { z := b } default { z := 0 }

New:

case 0 { z := b } default { revert(0, 0) }

Reason: Previously, when x = 0 and n > 0, the function returned 0 instead of reverting. This change ensures mathematical correctness by reverting in such cases.
Optimized conditional assignment for exponent parity check

Old:

switch mod(n, 2)
case 0 { z := b }
case 1 { z := x }

New:

z := b
if mod(n, 2) { z := x }

Reason: Replacing switch with an if statement reduces gas consumption and simplifies the code.
Removed duplicate declaration of let half := div(b, 2)

Old:

let half := div(b, 2) 
let half := div(b, 2) 

New:

let half := div(b, 2)

Reason: The duplicate declaration was unnecessary and increased execution costs.
Eliminated redundant overflow checks

Old:

if iszero(eq(div(xx, x), x)) { revert(0, 0) }
if and(iszero(iszero(x)), iszero(eq(div(xx, x), x))) { revert(0, 0) }

New:

if iszero(eq(div(xx, x), x)) { revert(0, 0) }

Reason: The second check was redundant and performed the same validation.
Removed unnecessary reassignments for rounding calculations

Old:

zx := add(zx, half);
z := div(zx, b);

New:

let zxRound := add(zx, half);
if lt(zxRound, zx) { revert(0, 0) }
z := div(zxRound, b);

Reason: The old code contained repeated assignments that increased gas costs without adding extra functionality.