♻️ Split the MQT dialect implementation

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Problem Statement

mlir/lib/Dialect/MQT/IR/MQTDialect.cpp combines dialect registration, typed attribute implementations, and attached-metadata verification. Separate these responsibilities using the existing QC/QCO source organization as a guide.

This is a follow-up to the review comment in #2219, not a prerequisite for that PR.

Proposed Solution

Start with two files:

• Keep dialect registration, operation/region attribute hooks, and their metadata helpers in MQTDialect.cpp.
• Move typed attribute definitions, verifiers, and TargetEnvAttr::query into MQTAttributes.cpp, keeping their private helpers together.

Update the existing MLIRMQTDialect CMake target. Preserve public APIs, attribute assembly, verification behavior, and diagnostics; no new abstraction or public helper API is needed. Keep naming and payload-version policy changes out of scope.

Acceptance: existing MQT IR and compiler tests pass, including attribute round trips and invalid-input cases; repository lint and C++ lint pass.