Linting check (Remove Warnings) fix

[aryang117]

Description

This fixes multiple all linting issue/warning except:

• All QuerySnapshot and QueryDocumentSnapshot warnings in database_service.dart as I don't know what kind of data is being received here
• getImage being depricated, changing this may impact a lot of other things and therefore has been not been fixed (edit_profile.dart)
• OwnerInfo class warning has not been fixed.

Fixes 32 of 47 warnings.

Fixes #99

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code of conduct of this project
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

• My changes generate no new warnings