🐛 Remove QCO/QTensor dependency cycles

[burgholzer]

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Description

Remove the QCO/QTensor library dependency cycles instead of relying on static archive repetition or bypassing LLVM's target ordering.

• Move the QTensor-specific qco.if scalarization pattern into QTensor's native dialect-wide canonicalization hook. QCO IR no longer includes or links QTensor.
• Remove the unused QTensor IR dependency on QTensorUtils. Keep ordinary one-way links from the utilities to QTensor IR and from QTensor IR to QCO IR.
• Move the five scalarization regressions to the QTensor suite. One runs the generic canonicalizer directly; the others exercise the existing cleanup pipeline.
• Remove the QIR runtime's redundant QTensor dependency.
• Use build-tree RPATHs for the LLVM IR test executables so they can find shared MQT Core libraries before installation.

This PR is based on main and is independent of #2336. It preserves the scalarization algorithm and compiler pipeline without adding a pass, library, or interface. No standalone changelog or upgrade entry is needed for this internal fix to unreleased compiler code.

Validation

• CMake's generated dependency graph has no cycles.
• All five scalarization regressions passed.
• Full Debug and Release C++ suites: 3,812 passed and one expected skip each.
• Debug with BUILD_MQT_CORE_SHARED_LIBS=ON: all 72 QIR runtime tests passed.
• uvx nox -s cpp-lint, uvx nox -s lint, and git diff --check passed.

An additional global BUILD_SHARED_LIBS=ON configuration probe is blocked by QDMI install-export declarations for MLIRQCODDFunctionality and MQTCompilerPipeline. That packaging issue is outside this change.

Codex assisted with dependency analysis, code relocation, and local validation.

Checklist

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
• I have added entries to the changelog for any noteworthy additions, changes, fixes, or removals.
• I have added migration instructions to the upgrade guide (if needed).
• The changes follow the project's style guidelines and introduce no new warnings.
• The changes are fully tested and pass the CI checks.
• I have reviewed my own code changes.

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[codecov]

Codecov Report

❌ Patch coverage is 97.77778% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...lib/Dialect/QTensor/IR/QTensorCanonicalization.cpp	97.7%	3 Missing ⚠️

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