Let audb.Dependencies methods return fix types

[hagenw]

This is a follow up on #24 and #25.

I changed the methods of audb.Dependencies to always return fix types which seems to me much safer as our current approach (even if the current approach makes semantically maybe more sense).

I also changed back the calculation of duration due to this:

>>> deps = audb.dependencies('audioset')
>>> timeit.timeit("deps()['duration'].sum()", number=10, setup="from __main__ import deps")
23.182365000000573
>>> timeit.timeit("sum([deps.duration(file) for file in deps.media])", number=10, setup="from __main__ import deps")
17.973571905007702

[codecov]

Codecov Report

Merging #27 (361cd3c) into master (217b1f7) will not change coverage.
The diff coverage is 100.0%.

Impacted Files	Coverage Δ
audb/core/info.py	100.0% <ø> (ø)
audb/core/dependencies.py	100.0% <100.0%> (ø)

[hagenw]

An alternative fix for duration() would be to add an if deps.duration(file) statement there as well as we did for other methods.
But I still think that it's easier to always return a value.

[frankenjoe]

But I still think that it's easier to always return a value.

agree