Block Result.unique() with Result.yield_per() for ORM results

The unique() + yield_per combination was only blocked when yield_per
was set via execution_options(yield_per=N); calling these as methods
on the result (e.g. result.unique().yield_per(N)) bypassed the check
and silently produced incorrect results.

Restructured _unique_filters on SimpleResultMetaData to be a callable
_create_unique_filters that receives the Result, allowing it to check
the yield_per state regardless of how it was activated.

Fixes: #13293
Change-Id: I7e6a5e5b2e1d4c8f9a0b3d6e7f1c2a4d5b8e9f0a