Federal prosecutors want Yasiel Puig to serve a lengthy stay behind bars after he was convicted of federal crimes earlier this year . A sentencing memorandum filed in a California court on Tuesday and obtained by The California Post on Wednesday shows that feds are requesting an 18-month prison sentence for the ex-Dodgers star who was found guilty in February of obstruction of justice and making false statements. Federal prosecutors want Yasiel Puig to serve a lengthy stay behind bars after he was convicted of federal crimes earlier this year. Frederick M. Brown for New York Post According to the filing, prosecutors are also asking for a sentence that includes three years probation as well as a $55,000 fine.…