feat: Add initial jeff-qiskitc converter tool

[aks8134]

Summary

Adds tools/jeff-qiskitc, a C++ tool that converts a jeff Module into a
Qiskit QkCircuit via the Qiskit C API. jeff -> Qiskit direction only, for
now. I'll add Qiskit -> jeff direction commit, after getting feedback from reviewers regarding
the design chosen here.

• WellKnownGate / PauliProductRotationGate / QubitGate (gate_converter.*)
  map jeff's QubitGate (wellKnown + controlled variants, and Pauli product
  rotations) onto the matching QkGate/QkPauliProductRotation.

• Op / QubitOp / FloatOp / AllocOp / MeasureNdOp / GateOp
  (circuit_converter.*); each capnp union kind modeled as its own type

• jeff_qiskitc.cpp is the entry point: a resource-counting pass sizes the
  QkCircuit up front, then a second pass builds it.

Currently covers QubitOp's alloc/measureNd/gate variants and Op's
qubit/float variants.

Testing

Added tools/jeff-qiskitc/tests/gate_conversion_test.cpp, exercising every
entry in WellKnownToQkGateMap/ControlledQkGateMap plus a handful of
Pauli product rotations, wired up via a new CMakeLists.txt
(ctest-registered). Locally: 216 assertions, 0 failures.

Open question for maintainers

This repo has no existing C++ build/CI setup. The new CMakeLists.txt needs QISKIT_C_DIR pointed at a
Qiskit C API install (headers + libqiskit.so), and I don't have visibility
into how CI should obtain that; build from source, a prebuilt release
artifact, or something else? Would appreciate guidance before wiring this
into CI.

Test plan

cmake -S tools/jeff-qiskitc -B build -DQISKIT_C_DIR=<path>
cmake --build build --target gate_conversion_test
ctest --test-dir build

AI Disclosures

All the library code and the design decisions have been made by me. For the tests and cmake files, I used claude code.