Add new decryptXX debugging functions

[jatZama]

In

fhevmjs/src/utils.ts

Line 89 in a9ee61c

decrypt64: (ciphertext: string) =>

we need to also add decrypt128 and decrypt256 functions, and potentially decryptEbytes64/128/256 ones. I already did this to test new types in mocked mode, but actually this would be very useful here as well if we want to do fast unit tests using the FHE private key.