[tree] return blob builders to pool after use

[max-hoffman]

I added a builder pool and never returned the objects, this adds the Put().

[coffeegoddd]

@max-hoffman DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
b024e60	ok	5937457

version	total_tests
b024e60	5937457

correctness_percentage
100.0

[max-hoffman]

#benchmark-import

[github-actions]

@max-hoffman workflow run: https://github.com/dolthub/dolt/actions/runs/9180691313

[coffeegoddd]

@max-hoffman DOLT

test_name	from_latency_median	to_latency_median	is_faster
tpcc-scale-factor-1	99.33	97.55	0

test_name	server_name	server_version	tps	test_name	server_name	server_version	tps	is_faster
tpcc-scale-factor-1	dolt	9165f6b	22.68	tpcc-scale-factor-1	dolt	b024e60	22.8	0

[coffeegoddd]

@max-hoffman DOLT

read_tests	from_latency_median	to_latency_median	is_faster
covering_index_scan	3.07	3.02	0
groupby_scan	17.63	17.63	0
index_join	5.28	5.18	0
index_join_scan	2.26	2.22	0
index_scan	53.85	53.85	0
oltp_point_select	0.52	0.52	0
oltp_read_only	8.58	8.58	0
select_random_points	0.83	0.83	0
select_random_ranges	0.99	0.99	0
table_scan	55.82	54.83	0
types_table_scan	137.35	137.35	0

write_tests	from_latency_median	to_latency_median	is_faster
oltp_delete_insert	6.79	6.79	0
oltp_insert	3.3	3.3	0
oltp_read_write	16.12	16.41	0
oltp_update_index	3.55	3.55	0
oltp_update_non_index	3.49	3.49	0
oltp_write_only	7.7	7.7	0
types_delete_insert	7.7	7.7	0

[coffeegoddd]

@max-hoffman DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
d360df3	ok	5937457

version	total_tests
d360df3	5937457

correctness_percentage
100.0

[reltuk]

Are we missing a bb.Reset() or something on the builders that go back into (or come out of?) the pool?

Generally LGTM.

[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
7924fba	ok	5937457

version	total_tests
7924fba	5937457

correctness_percentage
100.0

[coffeegoddd]

@max-hoffman DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
5c6afbe	ok	5937457

version	total_tests
5c6afbe	5937457

correctness_percentage
100.0

[coffeegoddd]

@max-hoffman DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
0a97f9d	ok	5937457

version	total_tests
0a97f9d	5937457

correctness_percentage
100.0

[coffeegoddd]

@max-hoffman DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
1394891	ok	5937457

version	total_tests
1394891	5937457

correctness_percentage
100.0