Feature: Add Magic Square game for Contextuality demonstration (#448)

* Add Contextuality magic square game implementation

* Remove TODOs

* some easy changes after dstrain115 review

* adding tests

* Add comments

* update docstring

* Literals and some of Eliott's docstrings

* typos

* Refactor _assign_choices_from_measurements

* change win matrix nomenclature

* tests

* SyntaxError

* solving errors?

* silly docs

* tests

* Update recirq/contextuality/magic_square_game.py

Co-authored-by: Michael Hucka <mhucka@google.com>

* Update recirq/contextuality/magic_square_game.py

Co-authored-by: Michael Hucka <mhucka@google.com>

* Update recirq/contextuality/magic_square_game.py

Co-authored-by: Michael Hucka <mhucka@google.com>

* Update recirq/contextuality/magic_square_game.py

Co-authored-by: Michael Hucka <mhucka@google.com>

* Update recirq/contextuality/magic_square_game.py

Co-authored-by: Michael Hucka <mhucka@google.com>

* Address review comments on Magic Square game

* Clean up unused Any import

* Apply suggestion from @mhucka

* Apply suggestion from @mhucka

* Update recirq/contextuality/magic_square_game.py

Co-authored-by: Michael Hucka <mhucka@google.com>

* correct docstrings

* correct docstrings again

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Co-authored-by: Eliott Rosenberg <eliottrosenbrg@google.com>
Co-authored-by: Michael Hucka <mhucka@google.com>

Author: 3 people