OK, OK, Sydney Sweeney has “great jeans,” and she’s using them to build an empire, but how does she stack up when regular women — you know, the ones not as voluptuous as she is — are concerned?   Backed by heavy hitters like Ben Schwerin of Coatue ,  SYRN (pronounced “siren”) is tapping into a saturated market of celebrity-owned brands, but I tell you, after going through its website, it’s clear she only has one type of clientele in mind.  I look at my tiny chest, and I find myself wondering,