Add extra helpers for string module

[samirsilwal]

Description:

This PR introduces a set of utility functions that handle common string and array operations, such as checking string prefixes and suffixes, removing duplicates from arrays, and trimming whitespace. These functions enhance code reusability and reduce redundancy for string and array manipulations.

Changes Included:

• startsWith(searchString):

Checks if a given string starts with a specific substring.
Returns false if the input is not a string.
Uses the built-in String.prototype.startsWith() method.

• endsWith(searchString):

Checks if a given string ends with a specific substring.
Returns false if the input is not a string.
Uses the built-in String.prototype.endsWith() method.

• unique(collection):

Extracts unique elements from an array.
Returns a new array with unique values.
Returns an empty string if the input is not an array or if it's empty.
Uses Set to filter out duplicates.

• trim(string):

Trims whitespace from both ends of a string.
Returns the trimmed string if the input is a valid string.
Returns the input as is if it’s not a string.
Uses String.prototype.trim().

Testing:

• Unit tests have been included for all functions to ensure correctness.
• Edge cases for invalid input types have been handled.