Implement new learning exercise: Protocols

This issue describes how to implement the `protocols` learning exercise for the Clojure track.

## Getting started

**Please please please read the docs before starting.** Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time. So, before diving into the implementation, please read up on the following documents:

- [The features of v3](https://github.com/exercism/v3/blob/main/docs/features-of-v3.md).
- [Rationale for v3](https://github.com/exercism/v3/blob/main/docs/rationale-for-v3.md).
- [What are concept exercise and how they are structured?](https://github.com/exercism/v3/blob/main/docs/concept-exercises.md)

Please also watch the following video:

- [The Anatomy of a Concept Exercise](https://www.youtube.com/watch?v=gkbBqd7hPrA).

## Goal

The goal of this exercise is to teach the student how protocols are used in Clojure.

I have an idea for this that I could be part of a really killer mini-syllabus: The student would build a tiny mathematics library, learning concepts by writing functions to solve equations.

## Learning objectives

This was inspired by Emmy, a Clojure computer algebra system: https://github.com/mentat-collective/emmy

One of Clojure's criminally (imo) underused domains is mathematics. This is a bit perplexing, because the ability to write mathematical expressions in a language based so strongly on such expressions is something that, to a mathematician, ought to be irresistible.

I'd like to use Clojure to do what Grant Sanderson (3blue1brown) does with Python in the world of maths exposition.

The emmy system is based heavily on protocols, which likely serves as an appropriate entry-point. The idea is to produce a library we'll codename "emmy-lite". Where emmy itself is designed for performance, ours will be designed for education.

## Out of scope

## Concepts

- `protocols`

## Prerequisites

- `basics`

## Resources to refer to

https://clojure.org/reference/protocols

Also check out https://github.com/Sophia-Gold/symbolic-algebra (also based on protocols!)

## Representer

## Analyzer

The [Clojure Analyzer](https://github.com/exercism/clojure-analyzer) is currently being implemented and contributions are welcome.

## Implementing

To implement a concept exercise, the following files must be created:

```
languages
└── clojure
└── exercises
└── concept
└──
├── .docs
| ├── instructions.md
| ├── introduction.md
| ├── hints.md
| └── after.md (optional)
├── .meta
| |── design.md
| └── Example.clj
├── .clj
└── _test.clj
```

## Help

If you have any questions while implementing the exercise, please post the questions as comments in this issue.