dynamic_partial_sum_product that uses sarkka_bilmes_product

[ordabayevy]

Addresses https://github.com/pyro-ppl/funsor/issues/293

group coded with @fehiepsi @fritzo

Currently failing under lazy interpretation because of some sarkka_bilmes_product bug.

• [x] pass existing tests for modified_partial_sum_product

[ordabayevy]

Sorry, my master branch was messed up so there are some changes that appear in minipyro example. I'll fix this soon (#536 too).

[eb8680]

Eagerly evaluated version looks good to me

[ordabayevy]

Thanks for reviewing @eb8680 !