text: Title: phase exponent ignored in approximate comparisons of `cirq.PhasedISwapPowGate`
  Body: **Description of the issue**
  
  `PhasedISwapPowGate` doesn't override the `_value_equality_approximate_values_` implementation it inherits from `EigenGate`, which means its phase exponent attribute isn't included in approximate comparisons
  
  the one exception is when its phase exponent is zero, in which case approximate comparison fails even when it shouldn't due to some of the same inconsistencies described for `cirq.PhasedXPowGate` in #6528
  
  **How to reproduce the issue**
  
  ```python
  gate0 = cirq.PhasedISwapPowGate(phase_exponent=0)
  gate1 = cirq.PhasedISwapPowGate(phase_exponent=1e-12)
  gate2 = cirq.PhasedISwapPowGate(phase_exponent=2e-12)
  gate3 = cirq.PhasedISwapPowGate(phase_exponent=0.345)
  
  assert cirq.approx_eq(gate1, gate2)  # ok
  assert cirq.approx_eq(gate1, gate0)  # fails, even though they are as close as the previous two
  assert cirq.approx_eq(gate1, gate3)  # passes, but shouldn't
  
  assert cirq.equal_up_to_global_phase(gate1, gate2)  # ok
  assert cirq.equal_up_to_global_phase(gate1, gate0)  # fails, even though they are as close as the previous two
  assert cirq.equal_up_to_global_phase(gate1, gate3)  # passes, but shouldn't
  ```
  
  **Cirq version**
  ```
  1.4.0.dev20240209232305
  ```