Return tau_effective from compute_Sv and update tau_effective handling

[LOCEANlloydizard]

Adding CW validation tests for tau_effective and return tau_effective from compute_Sv

• add tau_effective in the power-encoding path
• add EK80 CW validation tests for power-encoded data against Matecho and pyEcholab
• add EK80 CW validation tests for complex-encoded data against Matecho and Echoview
• compare both tau_effective and Sv outputs
• return tau_effective in compute_Sv for both power and complex encode paths

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.60%. Comparing base (6cf6cee) to head (8d5a52d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
echopype/calibrate/calibrate_ek.py	87.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1621      +/-   ##
==========================================
+ Coverage   85.58%   85.60%   +0.01%     
==========================================
  Files          79       79              
  Lines        6998     7021      +23     
==========================================
+ Hits         5989     6010      +21     
- Misses       1009     1011       +2     

Flag	Coverage Δ
integration	80.67% <87.50%> (+0.03%)	⬆️
unit	60.54% <87.50%> (+0.12%)	⬆️
unittests	85.50% <87.50%> (+0.01%)	⬆️

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