fix: subscriber callback not removed

[finger563]

Description

• Updated remove_subscriber implementation to use reference when erasing callback from list to ensure that it is properly erased from the shared state
• Added some warnings if removal occurs when topic or component are not found

Motivation and Context

Fixes a bug where the subscriber callback was not removed when it should have been, leading to the callback being called later.

How has this been tested?

Building and running within the esp-box-emu project.

Screenshots (if appropriate, e.g. schematic, board, console logs, lab pictures):

Types of changes

• 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)
• Documentation Update
• Hardware (schematic, board, system design) change
• Software change

Checklist:

• My change requires a change to the documentation.
• I have added / updated the documentation related to this change via either README or WIKI

Software

• I have added tests to cover my changes.
• I have updated the .github/workflows/build.yml file to add my new test to the automated cloud build github action.
• All new and existing tests passed.
• My code follows the code style of this project