[EXTERNAL] Update calculator_test.sh

[r0cketdyne]

Added set -euo pipefail to enforce safer scripting practices.

Improved variable scoping within the challenge function.

Simplified the function calls within the challenge function.

Refactored the test for the use of case statement.

Updated the invalid input tests to include better error handling.

Reorganized and improved the testing of operator functions.

Added a final message indicating the success of all tests.

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