feat: add reverse map data structure with value based sorting

[asart9O]

Description of Change

Added ReverseMap container with: insert(key, value) to build the map to_vector() to output a (key, value) list sorted.

Checklist

• [x] Added description of change
• [x] Added file name matches File name guidelines
• [x] Added tests and example, test must pass
• [x] Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• [x] Relevant documentation/comments is changed or added
• [x] PR title follows semantic commit guidelines
• [x] Search previous suggestions before making a new one, as yours may be a duplicate.
• [x] I acknowledge that all my contributions will be made under the project's license.

Notes: Implements "ReverseMap", a container that inverts key->value pairs and produces a vector of (key, value) sorted by value.