(RUF012) Fixed mutable class Defaults- Task 4

[drona-gyawali]

Part of #10196

• Prevents accidental modifications of mutable class attributes at the instance level.
• Aligns with project style guidelines enforced by Ruff.

Technical

• Updated mutable class attributes in 6 files to use typing.ClassVar for clarity and correctness.
• Added ClassVar annotations to mutable class attributes to ensure they are treated as class-level attributes.
• Ensured proper type hints for clarity and type safety.

Testing

Ran ruff check --select RUF012 to confirm no further warnings.

Screenshot

N/A

Stakeholders

@RayBB

[RayBB]

Looks great to me.
Now we need staff to review/merge.