Adds bosoniccircuit.py and its tests (#538)

* Adds bosoniccircuit.py and its tests

* Codefactor changes

* ran black

* More codefactor

* You guessed it: more codefactor

* Update strawberryfields/backends/bosonicbackend/bosoniccircuit.py

* Update strawberryfields/backends/bosonicbackend/bosoniccircuit.py

* Passes black

* adds disable

* puts disables in right places

* puts disables in right places

* Fix bug in if statement

* Apply suggestions from code review

Applies minor suggestions from Antal and Theo

Co-authored-by: antalszava <antalszava@gmail.com>
Co-authored-by: Theodor <theodor@xanadu.ai>

* Ran black

* Tidying code

Based on Antal and Theo's comments:
- more info in some docstrings
- clearer variable names
- extensive commenting of the generaldyne sampling algorithm

* Ran black

* Apply suggestions from code review

Co-authored-by: antalszava <antalszava@gmail.com>

* Changes how Y mat is created

- Applies Nico's suggestion

* Minor modifications based on code review

* Adds reset function to class init

- modifies/fixes associated tests

* Splits mb_squeeze into two cases

- Average map directly applied Gaussian CPTP map
- Single shot case simulates ancilla measurement and feedforward

* Add missing word to docstring

* Apply suggestions from code review

Co-authored-by: antalszava <antalszava@gmail.com>

* Tests for add/del modes and expandXY

-plus some docstring tidying

* Splits up gaussian transformations test

and runs black

* Docstring edit/rerunning codecov

* ci update

Co-authored-by: Nicolas Quesada <zeitus@gmail.com>
Co-authored-by: antalszava <antalszava@gmail.com>
Co-authored-by: Theodor <theodor@xanadu.ai>

.github/workflows/tests.yaml

@@ -35,6 +35,8 @@ jobs:
           access_token: ${{ github.token }}
 
       - uses: actions/checkout@v2
+        with:
+          fetch-depth: 2
 
       - name: Set up Python
         uses: actions/setup-python@v2