Better separation of CircuitData and PyCircuitData

[gadial]

AI/LLM disclosure

• I didn't use LLM tooling, or only used it privately.
• I used the following tool to help write this PR description:
• I used the following tool to generate or modify code:

[coveralls]

Coverage Report for CI Build 25154093382

Coverage increased (+0.008%) to 87.578%

Details

• Coverage increased (+0.008%) from the base build.
• Patch coverage: 12 uncovered changes across 2 files (107 of 119 lines covered, 89.92%).
• 12 coverage regressions across 5 files.

Uncovered Changes

File	Changed	Covered	%
crates/circuit/src/circuit_data.rs	93	82	88.17%
crates/qpy/src/circuit_reader.rs	20	19	95.0%

Coverage Regressions

12 previously-covered lines in 5 files lost coverage.

File	Lines Losing Coverage	Coverage
crates/circuit/src/parameter/symbol_expr.rs	4	73.8%
crates/qasm2/src/lex.rs	4	92.29%
crates/circuit/src/circuit_data.rs	2	87.21%
crates/circuit/src/parameter/parameter_expression.rs	1	90.53%
crates/qpy/src/circuit_reader.rs	1	78.88%

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Coverage Stats

Relevant Lines:	121286
Covered Lines:	106220
Line Coverage:	87.58%
Coverage Strength:	969405.1 hits per line

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💛 - Coveralls