[HWToBTOR2] Use APInt value directly in constant generation

[TaoBi22]

Currently creating a constant with any value that won't fit in an i64 will break HWToBTOR2 as it tries to fetch the value from an APInt and place it in an int64_t - not ideal if you have wires wider than 64 bits.

Breaking example:

hw.module @top() {
    hw.constant 111111111111111111111111111 : i100
}

This just swaps to using the APInt directly to print the value - AFAICT this will still yield correct BTOR2.

[dobios]

Good idea, the use of int64 was definitely limiting!