fix aggregate function

[jmoralez]

• Changes the aggregate function to handle both balanced and unbalanced series in the same way
• Deprecates the is_balanced argument
• Adds a simple test case that fails in the current main branch

Fixes #211
Fixes #224

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[candalfigomoro]

@jmoralez I think the is_balanced parameter was never included in a released version of the library (just the main branch on Git), so if you want to remove it, maybe you can just remove it instead of deprecating it.

[jmoralez]

@candalfigomoro it's in 0.3.0.

[candalfigomoro]

@candalfigomoro it's in 0.3.0.

@jmoralez You are right, I thought it was introduced with commit c107217 after version 0.3.0 but that commit only extended its usage.

[AzulGarza]

Thanks for this @jmoralez! LGTM :)