By Gertrude Chavez-Dreyfuss and Hannah Lang NEW YORK (Reuters) – Stablecoins, which are virtual tokens pegged to traditional currencies such as the U.S. dollar, held gains on Thursday in the midst of a sell-off in risk assets such as stocks and bitcoin after Russia launched a full-scale invasion of Ukraine. Most stablecoins were slightly higher on the day. Their market capitalization was up 0.3% at $182.5 billion, according to cryptocurrency data tracker coinmarketcap.com. Its daily trading volume, though, surged 75% to $108.1 billion. In contrast, both bitcoin and ether dropped to one-month l…