Update README benchmarks with fresh measured data

[timsehn]

Summary

Replace estimated multipliers with actual measured values. Split into read and write tables with honest commentary about index scan overhead and write path crashes.

🤖 Generated with Claude Code

[github-actions]

Sysbench-Style Benchmark: Doltlite vs SQLite

In-Memory

Reads

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_point_select	55	65	1.18
oltp_range_select	43	36	0.84
oltp_sum_range	16	15	0.94
oltp_order_range	4	8	2.00
oltp_distinct_range	7	8	1.14
oltp_index_scan	7	77	11.00
select_random_points	22	55	2.50
select_random_ranges	9	9	1.00
covering_index_scan	12	97	8.08
groupby_scan	55	57	1.04
index_join	6	38	6.33
index_join_scan	2	316	158.00
types_table_scan	12	14	1.17
table_scan	1	2	2.00
oltp_read_only	216	232	1.07

Writes

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_bulk_insert	29	35	1.21
oltp_insert	20	6118	305.90
oltp_update_index	46	crash	--
oltp_update_non_index	37	crash	--
oltp_delete_insert	43	60648	1410.42
oltp_write_only	20	8383	419.15
types_delete_insert	26	crash	--
oltp_read_write	194	8536	44.00

File-Backed

Reads

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_point_select	185	134	0.72
oltp_range_select	56	38	0.68
oltp_sum_range	25	19	0.76
oltp_order_range	6	6	1.00
oltp_distinct_range	8	13	1.62
oltp_index_scan	18	76	4.22
select_random_points	34	55	1.62
select_random_ranges	34	11	0.32
covering_index_scan	24	84	3.50
groupby_scan	58	58	1.00
index_join	12	41	3.42
index_join_scan	6	318	53.00
types_table_scan	11	16	1.45
table_scan	2	2	1.00
oltp_read_only	408	283	0.69

Writes

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_bulk_insert	34	1650	48.53
oltp_insert	22	7856	357.09
oltp_update_index	51	crash	--
oltp_update_non_index	36	crash	--
oltp_delete_insert	54	60059	1112.20
oltp_write_only	23	9998	434.70
types_delete_insert	28	crash	--
oltp_read_write	185	9958	53.83

10000 rows, single CLI invocation per test, workload-only timing via SQL timestamps.