Set up Jest unit testing

[ayshadogo]

Description:

• Jest is included by default in NestJS
• Add test scripts to package.json: test, test:watch, test:cov
• Write a basic test for AuthService.hashPassword using bcrypt

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[EmmanuelAdah]

I’d appreciate the opportunity to demonstrate my backend engineering expertise in resolving this issue.
I will configure the test, test:watch, and test:cov scripts in package.json and write a unit test for AuthService.hashPassword to verify password hashing with bcrypt.
Please assign this to me, and I’ll open a PR shortly.