dev: remove custom integer classes

[zmalatrax]

The use of custom classes to enforce signed and unsigned integers of a certain size reduces the readability of the code.
Plus it doesn't make much sense in TypeScript, it feels like trying to add C/Rust fixed-size integers to Typescript

• Converting a Felt to number and bigint must be doable:

  • Number(felt) works as expected because toString() is overridden (see javascript object coercition)
  • BigInt(value: string | number | bigint | boolean): bigint has a fixed signature, we must define a method to return the bigint value from Felt, which is done by Felt.toBigInt(): bigint

• Encoded instructions are defined on 64 bits. We can check that the instruction is indeed a number < $2^{64} - 1$, as in the python VM , or simply ignore the bits > 64. The encoded instruction is decoded with masks, solely working on the 64 LSBs.

• Values from the encoded instructions are truncated with masks of the expected size, there is no need to check that the offsets etc. are of the right size

• fromBiased should be a method of Instruction