fix: fix signed integer casting

[shpface]

Issue #, if available:

Description of changes: Prior to this change, signed integer casting worked based on sign+magnitude. This change will use two's complement.

• https://openqasm.com/language/types.html#casting-from-int-uint
• https://openqasm.com/language/types.html#casting-from-bit

Testing done:

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[codecov[bot]]

Codecov Report

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

Project coverage is 100.00%. Comparing base (a4d7f98) to head (6a28689).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #261 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 48 48 Lines 3712 3711 -1 Branches 889 890 +1 ========================================= - Hits 3712 3711 -1 ```

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