Merged PRs

dolt

3310: Split Iter.Next(), RowToSQL, and callback into separate threads
This PR expands on an optimization where we separate iter.Next() and RowToSQL + callback() into two separate threads. Now, iter.Next(), RowToSQL, and callback() all run in their own goroutines with corresponding buffered channels communicating between them.
Additionally, this PR tidys up the resultForDefaultIter and resultForValueIter code.
Benchmarks: #10103 (comment)
3309: unsafe methods in SQL and SQLValue
This PR adds unsafe string access to EnumType.SQLValue() and SetType.SQLValue().
Additionally, uses string concat over SPrintf().
Benchmarks: #10101 (comment)
3308: make IsNullable return true for nullable datetime functions
fixes #10092
I updated the datetime functions' IsNullable function based on whether they could return nil, using function_queries.go from #3305 as a reference.
We should probably do an audit of all our functions to make sure IsNullable is correct.

Read Tests	MySQL	Dolt	Multiple
covering_index_scan	1.86	0.55	0.3
groupby_scan	13.7	13.7	1.0
index_join	1.5	2.07	1.38
index_join_scan	1.5	1.34	0.89
index_scan	34.33	23.95	0.7
oltp_point_select	0.2	0.28	1.4
oltp_read_only	3.82	5.28	1.38
select_random_points	0.35	0.58	1.66
select_random_ranges	0.39	0.57	1.46
table_scan	34.95	28.16	0.81
types_table_scan	75.82	80.03	1.06
reads_mean_multiplier			1.09

Write Tests	MySQL	Dolt	Multiple
oltp_delete_insert	8.43	6.55	0.78
oltp_insert	4.18	3.19	0.76
oltp_read_write	9.22	11.65	1.26
oltp_update_index	4.25	3.25	0.76
oltp_update_non_index	4.25	3.19	0.75
oltp_write_only	5.28	6.32	1.2
types_delete_insert	8.58	6.91	0.81
writes_mean_multiplier			0.9

TPC-C TPS Tests	MySQL	Dolt	Multiple
tpcc-scale-factor-1	93.7	36.51	2.57
tpcc_tps_multiplier			2.57

Overall Mean Multiple	1.52