Fix RISC-V backend tests and update the flake

[DzmingLi]

1. Add short-circuit logical operators (Cexpr_and/Cexpr_or)

   • Implement proper short-circuit evaluation using conditional branches
   • AND: if lhs then rhs else false
   • OR: if lhs then true else rhs

2. Add T_bytes support in fixedarray operations

   • Handle Bytes as FixedArray[Byte] in Pfixedarray_get_item
   • Fixes "bad type in fixedarray_get_item" error

3. Add EverySingleElem support for FixedArray literals

   • Implement Pfixedarray_make with EverySingleElem kind
   • Enables array literals like [1, 2, 3, 4, 5]
   • Allocates buffer with length prefix and stores all elements

4. Fix list01/list02 recursive method calls

   • Update deprecated syntax: length(tail) → tail.length()
   • Update deprecated syntax: get(tail, i-1) → tail.get(i-1)
   • Fixes "value identifier unbound" errors

5. Update flake to automatically bundle the required core

6. **Update README **

   • Add RISC-V testing guide.
   • Modify nix develop guide.