go: sqle/cluster: Improve dolt_cluster_ack_writes_timeout_secs circuit breaker behavior.

[reltuk]

Previously, the circuit breaker only had an open and a closed state. It would only go from open to closed when the replication thread fully quiesced. This PR adds a half-open state, where it lets a single commit probe for replication success within the configured timeout. If that wait succeeds, the circuit breaker closes.

This lets high write throughput use cases reenable their configured replication waits even when writes arrive more requently than their typical replication delay.

[coffeegoddd]

@reltuk DOLT

read_tests	from_latency	to_latency	percent_change
covering_index_scan	2.3	2.3	0.0
groupby_scan	144.97	142.39	-1.78
index_join	1.93	1.96	1.55
index_join_scan	1.32	1.32	0.0
index_scan	219.36	223.34	1.81
oltp_point_select	0.25	0.25	0.0
oltp_read_only	5.0	5.0	0.0
select_random_points	0.51	0.51	0.0
select_random_ranges	0.64	0.64	0.0
table_scan	200.47	200.47	0.0
types_table_scan	467.3	458.96	-1.78

write_tests	from_latency	to_latency	percent_change
oltp_delete_insert	6.09	6.21	1.97
oltp_insert	3.13	3.13	0.0
oltp_read_write	11.24	11.24	0.0
oltp_update_index	3.3	3.3	0.0
oltp_update_non_index	2.97	3.02	1.68
oltp_write_only	6.21	6.21	0.0
types_delete_insert	6.79	6.79	0.0

[coffeegoddd]

@reltuk DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
fa6667c	ok	5937471

version	total_tests
fa6667c	5937471

correctness_percentage
100.0

[coffeegoddd]

@reltuk DOLT

test_name	from_latency_p95	to_latency_p95	percent_change
tpcc-scale-factor-1	45.79	45.79	0.0

test_name	from_server_name	from_server_version	from_tps	to_server_name	to_server_version	to_tps	percent_change
tpcc-scale-factor-1	dolt	041116f	53.23	dolt	fa6667c	53.2	-0.06

[zachmu]

LGTM