fix: iterative variable assignments in AutoQASM

Issue #, if available: https://github.com/amazon-braket/amazon-braket-sdk-python/issues/929, https://github.com/amazon-braket/amazon-braket-sdk-python/issues/933

Description of changes: Ensure that AutoQASM variables which are updated after declaration, including iteratively in a loop, are initialized properly.

Testing done: Added tests for new cases. Updated existing tests where variable declaration order changed. tox passes.

Note: If a variable is initialized with a Python variable and then updated iteratively in a loop, this scenario still does not work with the changes in this PR. A new issue has been added to the backlog for this: https://github.com/orgs/amazon-braket/projects/2/views/1?pane=issue&itemId=58435320.

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amazon-braket / amazon-braket-sdk-python