client: support reading multiple audio tracks (#179)

[aler9]

Fixes #179

[codecov]

Codecov Report

Attention: Patch coverage is 87.15596% with 14 lines in your changes missing coverage. Please review.

Project coverage is 73.13%. Comparing base (7b2e499) to head (855813d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
client_primary_downloader.go	87.50%	4 Missing and 3 partials ⚠️
client_stream_downloader.go	86.66%	4 Missing ⚠️
client_stream_processor_fmp4.go	85.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #200      +/-   ##
==========================================
+ Coverage   73.10%   73.13%   +0.02%     
==========================================
  Files          57       57              
  Lines        3964     3975      +11     
==========================================
+ Hits         2898     2907       +9     
- Misses        871      872       +1     
- Partials      195      196       +1     

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