Fix parameterized diagonal gates failing in circuit diagrams (#8404)

[jyothikacodes]

Fixes #8404

Description

In DiagonalGate, TwoQubitDiagonalGate, and ThreeQubitDiagonalGate, circuit_diagram_info previously converted
self._diag_angles_radians into a NumPy array prior to rounding. When diagonal gates contain SymPy symbols or
expressions, NumPy creates an object-dtype array and .round() attempts to call rint on Python objects, causing a
TypeError.

This PR preserves the tuple of angles and applies precision rounding only to non-parameterized elements, allowing
parameterized diagonal gates to render circuit diagrams properly.

Tests

Added regression tests verifying that parameterized diagonal gates with both numeric and symbolic angles render
circuit diagrams correctly with precision formatting:

• cirq-core/cirq/ops/diagonal_gate_test.py
• cirq-core/cirq/ops/two_qubit_diagonal_gate_test.py
• cirq-core/cirq/ops/three_qubit_gates_test.py

Testing Confirmation

│ Running pytest-changed-files, format-incremental, pylint-changed-files, and mypy passes all tests and checks locally
│ using Python 3.14 on Linux OS. Ready for review.

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[jyothikacodes]

Hello @NoureldinYosri @senecameeks , I’ve submitted a PR addressing this issue. I would really appreciate it if you could review it. Thank you for your time and consideration.