Migrate from poetry to uv

[PhilReinhold]

Convert pyproject.toml to PEP 621 with hatchling backend and a [dependency-groups] dev group. Replace poetry.lock with uv.lock, update CI workflows to use astral-sh/setup-uv, drop the install-poetry Makefile target, and switch the README install command to uv sync.

[PhilReinhold]

Note: this MR also touches src/ to fix newly-surfaced mypy errors

The poetry → uv switch isn't purely a packaging change — it forced a fresh dependency resolution, which pulled in two upgrades that have stricter type
signatures:

• mypy: 1.4.1 -> 1.20.2

• openqasm3 / openpulse: 0.5.0 -> 1.0.1

  Together these surfaced 67 new mypy errors, breaking down into three buckets:

  1. openqasm3 1.0 tightened AST signatures. Many AST nodes that used to accept list[Statement | Pragma] now require narrower types — e.g. Box.body:
     list[QuantumStatement], QuantumGate.qubits: list[IndexedIdentifier | Identifier], QuantumReset.qubits: IndexedIdentifier | Identifier,
     SubroutineDefinition.body: list[Statement]. oqpy's ProgramState.body legitimately holds list[Statement | Pragma], so we cast at the construction sites where we
     know the contents are valid.
  2. mypy 1.20 is stricter. It now flags missing type-arg on Iterable, numpy.floating not being assignable to float, implicit Optional defaults (PEP 484), and
     slice being a final class that can't subclass our protocols. Fixed via annotations, float(...) coercions, and adding slice to the AstConvertible union.
  3. One real bug. pulse.py:79 was passing ast.FrameType (the class) instead of ast.FrameType() (an instance) to OQFunctionCall's return_type. This silently
     broke the isinstance(extern.return_type, openpulse_types) check in _make_externs_statements. Caught now by the stricter signature.