Avery Hellman possesses an affable alto that’s quirky, as is the perspective from which Hellman writes. Hellman, whose grandfather founded the Hardly Strictly Bluegrass festival, is the rural California singer-songwriter behind the musical moniker ISMAY and the new album “Desert Pavement,” a captivating set with indeterminate antecedents. Hellman and producer/multi-instrumentalist Andrew Marlin create rich colors and hazy atmospherics in a …