Fix CW-based beamwidth scaling

[leewujung]

This PR addresses #997:

• fix the bug in scaling CW-based beamwidth_alongship and beamwidth_athwartship when frequency-dependent beamdwidth cal parameters do not exist in the data Vendor-specific group.
• add a test that ensures the scaling is applied correctly for the following parameters that all require scaling. Note in the descriptino below fc is center frequency of each broadband ping, fn is the channel nominal frequency.
  • beamwidth_alongship and beamwidth_athwartship: scale by fn/fc
  • angle_sensitivity_alongship and angle_sensitivity_athwartship: scale by fc/fn
  • equivalent_beam_angle: scale by (fn/fc)^2

Just to have things all in one place, we do not need to alter the test file test_calibrate_ek80.py, because (from my comment in #997):

Turns out for that particular file used in test_calibrate_ek80.py, there was no need to scale CW-based cal parameters (stored in the Sonar/Beam_groupX group) because those cal parameters happen to exist in a frequency-dependent form (stored in the Vendor-specific group) for the BB channels. (To elaborate: scaling is only needed if a particular parameter is not available in the frequency-dependent form and needs to be estimated from CW-based values.)

[codecov-commenter]

Codecov Report

Merging #998 (2350cf0) into dev (edc1d15) will increase coverage by 11.84%.
The diff coverage is 100.00%.

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@@             Coverage Diff             @@
##              dev     #998       +/-   ##
===========================================
+ Coverage   79.72%   91.56%   +11.84%     
===========================================
  Files          62       11       -51     
  Lines        5721      854     -4867     
===========================================
- Hits         4561      782     -3779     
+ Misses       1160       72     -1088     

Flag	Coverage Δ
unittests	91.56% <100.00%> (+11.84%)	⬆️

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Impacted Files	Coverage Δ
echopype/calibrate/cal_params.py	92.42% <100.00%> (+0.11%)	⬆️

... and 51 files with indirect coverage changes

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