Showcase felts and field operations

[tekkac]

Description

A felt, field element, is the first class citizens in Cairo. Write an exercise about the primitive type felt and the basic field operations it supports.

Resource:

• https://www.cairo-lang.org/docs/how_cairo_works/cairo_intro.html#field-elements

Acceptance criteria

• The exercise shows basic +, -, *, / operations on felts.
• The contract compiles and tests pass
• An exercise patch is generated