Optimize lookup functions by caching array accesses

[dduan]

Reduced redundant array accesses in tableValue, lookupTable, and
lookupArray functions. Each iteration now caches the lookup result
in a local variable instead of accessing the same array element
twice (once for keyHash and once for key).

This reduces array subscript overhead in hot paths during table
and key lookups, particularly beneficial for documents with many
nested tables.

[github-actions]

Comparing results between 'main' and 'pull_request'

Host 'runnervmh13bl' with 4 'x86_64' processors with 15 GB memory, running:
#18~24.04.1-Ubuntu SMP Sat Jun 28 04:46:03 UTC 2025

TOMLDecoderBenchmarks

Decode toml.io example metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (μs) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	67	68	68	69	73	87	135	7192
pull_request	67	68	68	69	74	88	123	7162
Δ	0	0	0	0	1	1	-12	-30
Improvement %	0	0	0	0	-1	-1	9	-30

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	625	625	625	625	625	625	625	7192
pull_request	625	625	625	625	625	625	625	7162
Δ	0	0	0	0	0	0	0	-30
Improvement %	0	0	0	0	0	0	0	-30

Parse toml.io example metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ns) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	5981	6111	6155	6203	6275	8239	38462	10000
pull_request	6101	6215	6255	6303	6363	10351	46296	10000
Δ	120	104	100	100	88	2112	7834	0
Improvement %	-2	-2	-2	-2	-1	-26	-20	0

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	9	10	10	10	10	10	10	10000
pull_request	9	10	10	10	10	10	10	10000
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

decode canada.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	266	266	266	266	267	267	267	4
pull_request	264	264	266	266	266	266	266	4
Δ	-2	-2	0	0	-1	-1	-1	0
Improvement %	1	1	0	0	0	0	0	0

Retains: results within specified thresholds, fold down for details.

Retains (K) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	1674	1674	1674	1674	1674	1674	1674	4
pull_request	1674	1674	1674	1674	1674	1674	1674	4
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

decode twitter.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (μs) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	8937	9003	9036	9060	9118	9331	9511	110
pull_request	8873	8970	8995	9036	9093	9544	10674	110
Δ	-64	-33	-41	-24	-25	213	1163	0
Improvement %	1	0	0	0	0	-2	-12	0

Retains: results within specified thresholds, fold down for details.

Retains (K) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	66	66	66	66	66	66	66	110
pull_request	66	66	66	66	66	66	66	110
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

parse GitHub events archive metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	165	167	167	169	179	179	179	6
pull_request	167	168	169	171	178	178	178	6
Δ	2	1	2	2	-1	-1	-1	0
Improvement %	-1	-1	-1	-1	1	1	1	0

Retains: results within specified thresholds, fold down for details.

Retains (K) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	77	77	77	77	77	77	77	6
pull_request	77	77	77	77	77	77	77	6
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

parse canada.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	16	17	18	18	18	19	19	57
pull_request	17	17	18	18	19	20	20	56
Δ	1	0	0	0	1	1	1	-1
Improvement %	-6	0	0	0	-6	-5	-5	-1

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	133	134	134	134	134	134	134	57
pull_request	133	134	134	134	134	134	134	56
Δ	0	0	0	0	0	0	0	-1
Improvement %	0	0	0	0	0	0	0	-1

parse twitter.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (μs) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	2716	2750	2761	2773	2789	2869	3278	355
pull_request	2726	2773	2789	2808	2824	2927	3363	352
Δ	10	23	28	35	35	58	85	-3
Improvement %	0	-1	-1	-1	-1	-2	-3	-3

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	1293	1294	1294	1294	1294	1294	1294	355
pull_request	1293	1294	1294	1294	1294	1294	1294	352
Δ	0	0	0	0	0	0	0	-3
Improvement %	0	0	0	0	0	0	0	-3