practice generators: fibonacci-generator

[szabgab]

Exercise related to #2367 to practice generators.

[BethanyG]

Hi @szabgab 👋🏽 ,

Thanks for filing this PR.

⚠️  Please be aware ⚠️

     This repo does not generally accept Pull Requests unless they follow our contributing guidelines and are:

     1️⃣     Small, contained fixes for typos/grammar/punctuation/code syntax on [one] exercise,
     2️⃣     Medium changes that have been agreed/discussed via a filed issue,
     3️⃣     Contributions from our help wanted issue list,
     4️⃣     Larger (previously agreed-upon) contributions from recent & regular (within the last 6 months) contributors.

    Pull Requests not in these categories will be closed. 😞

Please also note: new practice exercises are generally proposed and discussed in problem-specifications first, so that all tracks can potentially benefit from them. Once a new exercise is approved there by three maintainers, it becomes available for various language tracks to then implement. Only language-specific practice exercises are PR'd to an individual language track. Since JS, Go, Elixir, and many other languages have generators, this wouldn't be a candidate for a Python-specific practice exercise.

However, this exercise also looks as if it focuses on a specific concept or implementation (generators). For concept exercises, the specifications are quite different. Additionally, we already have someone who is working on our tracks generators concept exercise (Isee issue 2293), so this particular exercise would be conflicting with that in-progress work.

I am assuming that you will want to propose this exercise in problem-specificiations, so I will close it here. Apologies -- I am unable to transfer it for you.