Make `.slice()` in `GenericSpectrogram` usage clearer

[MohamedAli1937]

Describe the feature

Description:

I'm always frustrated when I try to manually slice spectrogram data because I have to figure out the correct array indices for both time and frequency axes, which is error-prone.

I would like it if the GenericSpectrogram.slice() method made slicing more clear and understandable for users.

This feature can gradually pave the way to coordinate-aware Spectra.

Exemple:

# Before slice method (manual slicing)
sliced_data = data[1:5, 1:4]
sliced_times = times[1:5]
sliced_freqs = freqs[1:4]

# After slice method
sliced_spec = spec.slice(time=(times[1], times[4]), freq=(freqs[1], freqs[3]))
print(sliced_spec.times)       # [t1, t2, t3, t4]
print(sliced_spec.frequencies) # [f1, f2, f3]

Proposed solution

No response