Remove unused thermocycler backend methods

[codewithdaniel1]

Summary

Removes unused thermocycler backend methods from ThermocyclerBackend and concrete backend implementations:

• get_block_target_temperature
• get_lid_target_temperature
• get_total_cycle_count
• get_total_step_count

The high-level Thermocycler now tracks target temperatures and protocol counts directly instead of requiring each backend to implement these methods.

Testing

python -m pytest pylabrobot/thermocycling --timeout=10

Result:

11 passed, 1 skipped