By Medha Singh and Lisa Pauline Mattackal (Reuters) – Bitcoin is beginning to reassert its dominance over challengers to its cryptocurrency crown. The original digital coin was assailed by thousands of new “altcoin” competitors in 2021 – from solana and polkadot to litecoin and dogecoin – raising the prospect of a rapid fragmentation of the crypto market. Yet bitcoin has stemmed its loss of market share this month, and begun to regain ground, as rattled investors seek the relative safety of the biggest crypto player while they contend with an aggressive Fed and talk of war in Europe. Bitcoin’s…