Fix naming convention and memory inefficiency in merge_sort.java

[Gorlesunilkumar]

1.Class name violates Java naming conventions // issue 1

public class merge_sort {

Problem: Java class names must start with a capital letter and follow PascalCase (e.g., MergeSort).
This is a core Java standard and affects readability and style consistency across the project.

Fix:

public class MergeSort {

2.Memory inefficiency due to new array creation in every merge // issue 2

int merge[] = new int[ei - si + 1];

Each recursive call of conquer() allocates a new temporary array, increasing memory usage unnecessarily.
This causes extra space complexity (O(n log n)) instead of O(n).

Fix:
Use a single global or reusable temporary array for all merges to improve efficiency:

int[] temp = new int[arr.length];
mergeSort(arr, temp, si, ei);