Avoid type erasure need in accumulation publishers

[defagos]

Pull request

Description

This PR improves Publishers.AccumulateLatestMany signature so that it can be used without type erasure.

Changes made

• Add a UT validating prototype changes (the content of the UT is itself not that relevant and barely tests Publishers.AccumulateLatestMany behavior).
• Update method prototypes.

This accumulator publisher is now also part of Pillarbox Core package. I thoroughly tested its behavior there and I propose to backport prototype improvements to SRG Data Provider in the meantime.

Publisher testing support is far better in Pillarbox. For this reason I decided not to add other tests which are made in Pillarbox.

[pyby]

@defagos Thanks to shared this improvement to the library.