chore!: Remove add_file and file_reader from FileManager

[kevaundray]

Description

This removes FileManager from add_file and uses add_file_with_source

Problem*

Resolves

Summary*

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [Exceptional Case] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[jfecher]

What is the reasoning for this change?

[kevaundray]

What is the reasoning for this change?

This is a follow-up to #3760 -- I made it a separate PR just so that I could modularise the changes being made, but its intended to be merged into 3760 and then 3760 can be seen as one PR.

This PR essentially removes add_file which is no longer being used because of 3760.

[kevaundray]

What is the reasoning for this change?

This is a follow-up to #3760 -- I made it a separate PR just so that I could modularise the changes being made, but its intended to be merged into 3760 and then 3760 can be seen as one PR.

This PR essentially removes add_file which is no longer being used because of 3760.

What is the reasoning for this change?

This is a follow-up to #3760 -- I made it a separate PR just so that I could modularise the changes being made, but its intended to be merged into 3760 and then 3760 can be seen as one PR.

This PR essentially removes add_file which is no longer being used because of 3760.

Should have made this clear good ser