Implement BRMI and BRPL branch instructions

[sql-hkr]

These instructions handle conditional jumps based on the N (Negative) flag in the status register, which indicates whether the result of the last arithmetic or logic operation was negative.

Tasks:

• Implement BRMI to branch when N = 1.
• Implement BRPL to branch when N = 0.
• Add corresponding unit tests verifying correct behavior for negative and positive values.

References:

• [1] AVR® Instruction Set Manual