fix: [#2046] Replace slice(1) with index-based traversal in QuerySelector

[TrevorBurnham]

Fixes #2046

This PR optimizes QuerySelector by replacing inefficient array operations with index-based traversal and accumulator patterns, eliminating unnecessary memory allocations during recursive DOM traversal.

Changes

1. Adds a selectorIndex parameter to matchSelector, findAll, and findFirst to avoid slice(1) array copies on each recursive call.

2. Eliminates items.reverse() in matches() by traversing the selector array backwards (from length - 1 to 0) instead of reversing the array first.

3. Changes findAll from returning arrays (with concat()) to using an accumulator array parameter, eliminating O(n) array copies on each recursive step.

4. Removes redundant children.indexOf(child) calls in findAll and findFirst by using the existing loop index i.

Before

// In matches():
const reversedItems = items.reverse();  // Mutates array
const result = this.matchSelector(element, reversedItems, 0, ...);

// In findAll - creates new arrays on every recursive call:
matched = matched.concat(
    this.findAll(rootElement, children, selectorItems.slice(1), ...)
);

// Redundant indexOf:
const index = children.indexOf(child);
for (let j = index + 1; ...)

After

// In matches():
const result = this.matchSelector(element, items, items.length - 1, ...);

// In findAll - pushes directly to accumulator:
this.findAll(rootElement, children, selectorItems, nextIndex, ..., matched);

// Uses existing loop index:
for (let j = i + 1; ...)

Impact

• Eliminates O(n) array copies from slice(1) and concat() on each recursive step
• Removes array reversal overhead in matches()
• Removes O(n) indexOf lookups in sibling traversal
• Reduces GC pressure for complex selectors and deep DOM trees
• All 143 QuerySelector tests pass