Iterate options per path for baked cache key

Iterate options per path for baked cache key

Fixed an issue that was both a performance regression in 1.2 as well as an
incorrect result regarding the "baked" lazy loader, involving the
generation of cache keys from the original :class:`.Query` object's loader
options.  If the loader options were built up in a "branched" style using
common base elements for multiple options, the same options would be
rendered into the cache key repeatedly, causing both a performance issue as
well as generating the wrong cache key.  This is fixed, along with a
performance improvement when such "branched" options are applied via
:meth:`.Query.options` to prevent the same option objects from being
applied repeatedly.

Change-Id: I955fe2f50186abd8e753ad490fd3eb8f017e26f9
Fixes: #4270