pyqir opaque pointers + docs & refs updates

[ryanhill1]

Summary of changes

This pull request introduces support for SQUIN conversions and updates compatibility for newer versions of PyQIR, including handling both typed and opaque pointers. Documentation and metadata have been updated to reflect these changes, and test workflows now cover both pyqir 0.10.x and 0.12+ versions. The most important changes are grouped below.

SQUIN integration and documentation updates:

• Added SQUIN conversion support, including new installation instructions (README.md, pyproject.toml, CITATION.cff, docs/index.rst, docs/api/qbraid_qir.squin.rst).

PyQIR compatibility improvements:

• Introduced _pyqir_compat.py to provide a unified API for both typed and opaque pointer versions of PyQIR (0.10.x and 0.12+), and updated Cirq visitor logic to use this compatibility layer.

Test workflow enhancements:

• Modified GitHub Actions workflow to run tests separately for pyqir 0.10.x and 0.12+, combine coverage, and generate unified reports.

Metadata and dependency updates:

• Updated project metadata, dependencies, and classifiers to support new Python and PyQIR versions, and reflect SQUIN support.

Changelog and example updates:

• Cleaned up and reorganized CHANGELOG.md, removing old release details and referencing the Releases page. Updated submodule reference in examples.

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
qbraid_qir/_pyqir_compat.py	92.00%	2 Missing ⚠️

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