Effect of optimistic_lock::try_read_lock testing once in the straight path

baseline commit, patch

All tests filtered for unodb::olc_db.

• micro_benchmark_key_prefix: 2% slowdown (unpredictable_get_shared_length) to 2% speedup (unpredictable_cut_key_prefix)
• micro_benchmark_n4: 2% slowdown (full_n4_random_deletes/100) to 6% speedup (full_n4_sequential_insert/32768)