feature: add support for typecasting

[abidart]

Issue #, if available: Related to #10.

Description of changes: In an attempt to add support for int and float conversion, I made 3 changes:

• a typecast converter that converts int and float calls
• a typecast operator that adds a different behavior to int and float calls when they act on a qasm type
• a line in the transpiler file to incorporate the typecast transformer

The goal is to add a functionality such that the following two compile to the same QASM instructions, or very similar:

syndrome = int(measure([0,1]))
################################
a1 = aq.IntVar(measure(1))
a0 = aq.IntVar(measure(0))
syndrome = 2*a1 + a0

Testing done:

• I know that the current code fails when the call to int or float is nested, for example syndrome = 2 * int(measure([0,1])). I need to fix that.
• The current changes pass tox -e unit-tests

Merge Checklist

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• [x] I have read the CONTRIBUTING doc
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[abidart]

I added 3 unit tests but I was not sure if they should go into test_api.py, test_operator.py, or test_converter.py, what do you think? Also, do you think that the expected_irs look reasonable?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (f83bb15) to head (f50afec). Report is 8 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #27 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 47 49 +2 Lines 2057 2090 +33 Branches 343 345 +2 ========================================= + Hits 2057 2090 +33 ```

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[rmshaffer]

I added 3 unit tests but I was not sure if they should go into test_api.py, test_operator.py, or test_converter.py, what do you think?

@abidart Probably test_operators.py makes the most sense. test_api.py is getting too large and needs to be split apart at some point.

[abidart]

@rmshaffer I pushed a new commit with cosmetic changes based on the review from #29 anticipating similar comments.