and mocked coverage for inspiral and merger-ringdown generators

- Add unit tests for inspiral and MR mode generation utilities using
mocked lalsimulation / delegated generators.
- Add deterministic unit tests for waveform utilities, blending helpers,
and legacy fitting functions without using mocks.

utils.py
* verify f22/x roundtrip consistency across x and mass ranges
* verify f22 scales as M^-1
* verify Schwarzschild ISCO frequency for zero spins
* verify prograde spins increase ISCO frequency
* verify retrograde spins decrease ISCO frequency
* verify monotonic inputs produce no detected peaks
* verify sinusoidal inputs return expected peak locations
* verify equatorial-plane polarization reconstruction for (2,2) mode
* verify face-on symmetry gives hx = 0
* verify polarization linearity under mode scaling

blend.py
* verify first-value lookup on constant arrays
* verify first/last index lookup on increasing arrays
* verify first/last symmetry properties
* verify amplitude extraction for known complex inputs
* verify amplitude for real-valued inputs
* verify phase unwrapping for linear complex phase
* verify constant-phase inputs produce flat phase
* verify frequency recovery from linear phase evolution
* verify decreasing phase produces negative frequencies
* verify mismatch is zero for identical waveforms
* verify mismatch is one for orthogonal waveforms
* verify mismatch remains within [0, 1]
* verify blended series matches endpoints correctly
* verify blended series smoothness across transition region
* verify blended series output length
* verify phase alignment reduces mismatch
* verify inverse alignments cancel net phase shift

legacy.py
* verify zero polynomial coefficients return unity
* verify quadratic polynomial evaluation for known coefficients
* verify equal numerator/denominator ratio polynomial returns unity
* verify fitting functions remain positive for η ∈ (0, 0.25]
* verify fitting functions are finite at η = 0.01 and η = 0.25

Included test coverage:

* TestGetInspiralEsigmaModesWithMock (7 tests)
  - verify returned dict contains requested (l,m) key
  - verify include_conjugate_modes=True/False controls (l,-m)
  - verify default return type is pycbc.TimeSeries
  - verify return_pycbc_timeseries=False returns numpy arrays
  - verify distance conversion from Mpc to SI before C call
  - verify mode generation called once per unique mode

* TestEccentricityAtReferenceFrequencyWithMock (2 tests)
  - verify nearest-index lookup logic for x_ref
  - verify returned eccentricity matches argmin|x - x_ref|

* TestGenerateLalsimModesWithMock (5 tests)
  - verify missing approximant propagates AttributeError -> IOError
  - verify linked-list traversal filters requested modes only
  - verify all requested modes are returned
  - verify unrequested modes are ignored
  - verify extracted mode data is returned as numpy arrays

* TestGetMrModesWithMock (4 tests)
  - verify f_ref=None defaults to f_lower
  - verify coa_phase=None defaults to 0.0
  - verify NRSur7dq4 routes to _generate_lalsim_modes
  - verify SEOBNRv5HM routes to _generate_pyseobnr_modes