fix: clarify signed & unsigned for jump insts

[hsqStephenZhang]

content

fix the signed/unsigned comparisons in several jump instructions in the execute_program function

Key changes include:

• Added a new macro unsigned_u64! to convert immediate values to unsigned 64-bit integers (i can be simply written as inst.imm as u32 as u64, the macro is just for better readability, i can change it back to the simpler version if you wish)
• Updated the implementation of several jump instructions (JEQ_IMM, JGT_IMM, JGE_IMM, JLT_IMM, JLE_IMM, JNE_IMM) to use the new unsigned_u64! macro, ensuring correct handling of unsigned comparisons.

reference

• https://docs.kernel.org/bpf/standardization/instruction-set.html#jump-instructions