Consider updating `DEFAULT_TEMP` from 300 K to 298.15 K

[maxentile]

Migrated from https://github.com/proteneer/timemachine/pull/825#discussion_r970037993

Ideally thermodynamic parameters should be as consistent as possible between simulation conditions and experimental conditions, but (1) small differences may be inconsequential, (2) there may be overriding considerations.