Fix: connection.rs error and improve error handling

[nafisatou]

What This PR Does

• Fixes type inference error in connection.rs by adding explicit Result<()> type
• Replaces manual Err(format!(...)) with anyhow::bail!() for cleaner error handling
• Removes compiler warnings from unused mut variables
• Adds doc comments for better code readability

Why
This ensures that the project compiles properly and improves overall code

[bansikah22]

@nafisatou you should use the 2024 and not go back to 2021

[Nkwenti-Severian-Ndongtsop]

@nafisatou please ensure your PR passes all the checks
I can see you have formatting issues.
Always try to run the commands in this workflows manually before requesting a pull, that is

• cargo fmt --check
• cargo clippy -- -D warnings
  You can also check the workflow to know what it checks in your code

[micheal-ndoh]

@nafisatou run the ci-local.sh script to check if your code is well formatted before pushing dr

[Christiantyemele]

@nafisatou fix the failing pipeline with cargo fmt --all