Restore and harden commit message whitespace cleanup

[elianddb]

• Add CleanCommitMessage: strips trailing whitespace per line, drops leading and trailing blank lines, collapses runs of internal blank lines to one, and preserves leading whitespace on content lines.
• Place cleanup at user-facing entry points commit, rebase, and merge.

[coffeegoddd]

@elianddb DOLT

read_tests	from_latency	to_latency	percent_change
covering_index_scan	0.54	0.54	0.0
groupby_scan	9.91	9.91	0.0
index_join	1.82	1.82	0.0
index_join_scan	1.32	1.32	0.0
index_scan	22.28	21.89	-1.75
oltp_point_select	0.25	0.25	0.0
oltp_read_only	5.09	5.09	0.0
select_random_points	0.5	0.5	0.0
select_random_ranges	0.56	0.56	0.0
table_scan	22.28	22.28	0.0
types_table_scan	46.63	65.65	40.79

write_tests	from_latency	to_latency	percent_change
oltp_delete_insert	6.32	6.32	0.0
oltp_insert	3.07	3.13	1.95
oltp_read_write	11.04	11.04	0.0
oltp_update_index	3.19	3.19	0.0
oltp_update_non_index	3.02	3.02	0.0
oltp_write_only	5.99	5.99	0.0
types_delete_insert	6.67	6.91	3.6

[coffeegoddd]

@elianddb DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
53ab3f8	ok	5937471

version	total_tests
53ab3f8	5937471

correctness_percentage
100.0

[coffeegoddd]

@elianddb DOLT

test_name	from_latency_p95	to_latency_p95	percent_change
tpcc-scale-factor-1	54.83	54.83	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	090798e	44.72	dolt	9f62252	43.97	-1.68

[coffeegoddd]

@elianddb DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
7b41a1f	ok	5937471

version	total_tests
7b41a1f	5937471

correctness_percentage
100.0

[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
a44436e	ok	5937471

version	total_tests
a44436e	5937471

correctness_percentage
100.0

[coffeegoddd]

@elianddb DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
9f62252	ok	5937471

version	total_tests
9f62252	5937471

correctness_percentage
100.0