PBKDF2_ ITERATIONS
Number of PBKDF2 iterations specified by BIP-39.
Per BIP-39: "To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string 'mnemonic' + passphrase (again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048."