Add `multiply`, `and_`, and `or_`

[MaxGhenis]

e.g. to replace this:

would_claim_CTC = benunit("would_claim_CTC", period)
claims_legacy_benefits = benunit("claims_legacy_benefits", period)
return would_claim_CTC & claims_legacy_benefits

with this:

return and_(benunit, period, ["would_claim_CTC", "claims_legacy_benefits"])

or if an or condition:

return or_(benunit, period, ["would_claim_CTC", "claims_legacy_benefits"])

[nikhilwoodruff]

Adding all but multiply_ - can we think of an example that wouldn't be covered by and_?

[MaxGhenis]

Not actual policy but something like this (suppose CB is means-tested so the amount is a variable rather than parameter):

total_child_benefit = multiply_(
    benunit,
    period,
    ["child_benefit_eligible", "number_of_children", "child_benefit_amount_per_child"]
)

[nikhilwoodruff]

OK, not sure that specific example works (number of children is probably group-level, amount per child probably person-level) but I've added multiply (as an alias of and_).