Re-organise pipeline execute commands to use same internal function

[adam-fowler]

This is in preparation for transaction changes which ended up duplicating the code in the _execute function as well
It's also an allocation improvement

[github-actions]

❌ Benchmark comparison failed with error ❌

Summary

==============================================================================
Threshold deviations for ValkeyBenchmarks:Connection: Pipeline array benchmark
==============================================================================

Malloc (total) (K, %)	main	pull_request	Difference %	Threshold %
p25	37	33	-11	5
p50	38	34	-10	5
p75	43	34	-20	5

========================================================================
Threshold deviations for ValkeyBenchmarks:Connection: Pipeline benchmark
========================================================================

Malloc (total) (K, %)	main	pull_request	Difference %	Threshold %
p25	36	33	-10	5
p50	37	33	-11	5
p75	37	34	-9	5

New baseline 'pull_request' is BETTER than the 'main' baseline thresholds.

Full Benchmark Comparison

Comparing results between 'main' and 'pull_request'

Host '52385896dc8a' with 4 'x86_64' processors with 15 GB memory, running:
#18~24.04.1-Ubuntu SMP Sat Jun 28 04:46:03 UTC 2025

ValkeyBenchmarks

Client: GET benchmark metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	82	82	84	85	85	85	85	6
pull_request	81	85	85	85	87	87	87	6
Δ	-1	3	1	0	2	2	2	0
Improvement %	1	-4	-1	0	-2	-2	-2	0

Client: GET benchmark | parallel 20 | 20 concurrent connections metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	96	99	103	107	110	111	111	23
pull_request	95	98	103	107	109	119	119	24
Δ	-1	-1	0	0	-1	8	8	1
Improvement %	1	1	0	0	1	-7	-7	1

Connection: GET benchmark metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	4	4	4	4	4	4	4	8
pull_request	4	4	4	4	4	4	4	8
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

Connection: GET benchmark – NoOpTracer metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	7	8	8	10	10	10	10	8
pull_request	7	8	8	10	10	10	10	8
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

Connection: Pipeline array benchmark metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	37	37	38	43	45	45	45	5
pull_request	33	33	34	34	34	34	34	6
Δ	-4	-4	-4	-9	-11	-11	-11	1
Improvement %	11	11	11	21	24	24	24	1

Connection: Pipeline benchmark metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	36	36	37	37	37	37	37	5
pull_request	33	33	33	34	34	34	34	6
Δ	-3	-3	-4	-3	-3	-3	-3	1
Improvement %	8	8	11	8	8	8	8	1

HashSlot – {user}.whatever metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	0	0	0	0	0	0	0	18
pull_request	0	0	0	0	0	0	0	18
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

ValkeyCommandEncoder – Command with 7 words metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	0	0	0	0	0	0	0	742
pull_request	0	0	0	0	0	0	0	735
Δ	0	0	0	0	0	0	0	-7
Improvement %	0	0	0	0	0	0	0	-7

ValkeyCommandEncoder – Simple GET metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	0	0	0	0	0	0	0	1886
pull_request	0	0	0	0	0	0	0	1870
Δ	0	0	0	0	0	0	0	-16
Improvement %	0	0	0	0	0	0	0	-16

ValkeyCommandEncoder – Simple MGET 15 keys metrics

Malloc (total): results within specified thresholds, fold down for details.

Malloc (total) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	0	0	0	0	0	0	0	348
pull_request	0	0	0	0	0	0	0	358
Δ	0	0	0	0	0	0	0	10
Improvement %	0	0	0	0	0	0	0	10