[WIP] Arc PyDAGCircuit - #16630
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The following commit splits the representations of `DAGCircuit` into: - `DAGCircuit` representing the rust-native implementation of the `DAG` excluding its metadata. - `PyDAGCircuit` the version that gets exposed to Python. `PyDAGCircuit` does not implement `Deref<DAGCircuit>` due to future plans requiring us to implement a reference counted `Circuit` for the Python version of the DAG.
The following commits make sure we preserve the metadata of the `DAGCircuit` in passes where the instance is copied. This includes: - `CommutativeOptimization` - `ConvertToPauliRotations` - `DisjointLayout` - `ElidePermutations` - `LitinskiTransformation` - `Split2QUnitaries` - `TwoQubitPeepholeOptimization` - `BasisTranslator` - `SabreLayout` - `SabreRouting` - `UnitarySynthesis`
This commit moves the `name` attribute to exist only within `PyDAGCircuit` since it is Python exclusive metadata. This commit also adds constructors with metadata from other `PyDAGCircuit` instances and a `DAGCircuit` from rust: - `from_dagcircuit` which also accepts optional `metadata` and `name`. - `from_dagcircuit_with_cloned_metadata` which accepts a reference to the `PyDAGCircuit` and copies over the attributes for the user. The transpiler passes that don't perform transformations in place have been updated to use this model.
Some auxiliary methods would need to immutably or mutably obtain the dag and therefore should only remain as auxiliary methods to the `DAGCircuit` instead of the `PyDAGCircuit` instance.
The methods will now be called `try_read` and `try_write` and are fallible. This commit refactors the methods and updates their usage.
- This introduces a clone which we will try and resolve later.
Provisionally this method has been split to have a python version, although the original is not fully independent of Python either. This allows the C API version to avoid using `PyDAGCircuit`.
These attributes are all public, so no need to provide immutable views.
The folllowing commti replaces the internals of `PyDAGCircuit` to include an atomic-reference-counted cell that encloses a Read-Write Lock to guarantee that the `DAG` instance may still be mutable afterwards. This commit doesn't work on its own and a follow-up commit fixing the behavior of `PyDAGCircuit` on every transpiler pass.
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