Simplify an opened multiple angle before judging it (#557) - #732

The reporter's second expression is 0 and came back as a sum of five
terms. Its first was already handled -- opening sin(2t) up is what
settles it -- and the second needs the same opening to survive one step
further than it did.

Opening a multiple angle is offered as a candidate rather than taken,
because written out sin(4x) is longer than it started, and the
complexity metric decides. That judgement is right; what was wrong is
the form it was asked to judge. The opened form was handed to the
trigonometric rules only, which settles an expression that is already a
single term. This one is a quotient, and it cancels only once its terms
are over a common denominator -- and the passes that build one run
earlier in the loop, while the angles are still shut. So the metric saw
the opened form with none of its payoff collected and rightly rejected
it as the longer of the two.

It is now simplified in full first, which is what Expand and Factorize
already get two lines above, and for the same reason. Expanded as well:
the cancellation here only appears once the products are multiplied
out, so `sin(t)^6 - (2 sin(t) cos(t))^2 sin(t)^4/4` over `sin(t)^8` has
to be opened before it reads as 1.

Only one candidate, not two. Offering the unexpanded opening as well
made no difference to any expression measured and doubled the added
cost.

Measured: the reporter's second expression from a sum of five terms to
`0 provided not sin(t) = 0`, in 269 ms. Multiple angles that do not
cancel keep their compact form -- sin(4x), cos(6x) and sin(3x) are
unchanged, and sin(8x)cos(8x) still collapses to sin(16x)/2 -- and cost
roughly 1.2 to 2 times what they did, in the tens of milliseconds; only
an expression that contains a multiple angle pays anything. Full suite
4858 passed / 0 failed, F# 130/130, corpus 112/117 with 0 wrong, 0
error, 0 timeout, and unchanged in total time.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>