test: add required Loki query semantics matrix

[szibis]

Summary

• add a manifest-driven Loki query semantics matrix and run it in the required PR workflow
• expand positive and negative LogQL coverage for selectors, filters, parsers, metric aggregations, instant post-aggregations, and binary operations
• fix parity gaps uncovered by the matrix for instant post-aggregation handling, metric stream identity preservation, and stats label shaping

Validation

• Go test: No tests found
• Go test: No tests found
• Go test: No tests found

Follow-up

• bare parser-metric cardinality after parser stages is a real Loki parity bug, not an accepted unsupported case; this PR documents it explicitly and keeps it out of the required gate until the proxy matches Loki for that shape

[github-actions]

PR Quality Report

Compared against base branch main.

Coverage and tests

Signal	Base	PR	Delta
Test count	1811	1838	27
Coverage	89.1%	88.8%	-0.3% (regressed)

Compatibility

Track	Base	PR	Delta
Loki API	100.0%	11/11 (100.0%)	0.0% (stable)
Logs Drilldown	100.0%	17/17 (100.0%)	0.0% (stable)
VictoriaLogs	100.0%	11/11 (100.0%)	0.0% (stable)

Compatibility components

Track	Component	Base	PR	Delta
Loki API	label_values	2/2 (100.0%)	2/2 (100.0%)	0.0% (stable)
Loki API	labels	4/4 (100.0%)	4/4 (100.0%)	0.0% (stable)
Loki API	metrics	2/2 (100.0%)	2/2 (100.0%)	0.0% (stable)
Loki API	otel	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
Loki API	query_range	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
Loki API	series	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
Logs Drilldown	detected_fields	11/11 (100.0%)	11/11 (100.0%)	0.0% (stable)
Logs Drilldown	label_values	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
Logs Drilldown	level_volume	2/2 (100.0%)	2/2 (100.0%)	0.0% (stable)
Logs Drilldown	patterns	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
Logs Drilldown	service_logs	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
Logs Drilldown	service_selection	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
VictoriaLogs	detected_fields	4/4 (100.0%)	4/4 (100.0%)	0.0% (stable)
VictoriaLogs	field_values	3/3 (100.0%)	3/3 (100.0%)	0.0% (stable)
VictoriaLogs	index_stats	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
VictoriaLogs	stream_translation	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
VictoriaLogs	synthetic_labels	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)
VictoriaLogs	volume_range	1/1 (100.0%)	1/1 (100.0%)	0.0% (stable)

Performance smoke

Lower CPU cost (ns/op) is better. Lower benchmark memory cost (B/op, allocs/op) is better. Higher throughput is better. Lower load-test memory growth is better. Benchmark rows are medians from repeated samples.

Signal	Base	PR	Delta
QueryRange cache-hit CPU cost	1333.0 ns/op	1365.0 ns/op	+2.4% (stable)
QueryRange cache-hit memory	200.0 B/op	200.0 B/op	0.0% (stable)
QueryRange cache-hit allocations	7.0 allocs/op	7.0 allocs/op	0.0% (stable)
QueryRange cache-bypass CPU cost	1693.0 ns/op	1628.0 ns/op	-3.8% (stable)
QueryRange cache-bypass memory	271.0 B/op	272.0 B/op	+0.4% (stable)
QueryRange cache-bypass allocations	7.0 allocs/op	7.0 allocs/op	0.0% (stable)
Labels cache-hit CPU cost	715.9 ns/op	692.0 ns/op	-3.3% (stable)
Labels cache-hit memory	48.0 B/op	48.0 B/op	0.0% (stable)
Labels cache-hit allocations	3.0 allocs/op	3.0 allocs/op	0.0% (stable)
Labels cache-bypass CPU cost	826.6 ns/op	852.5 ns/op	+3.1% (stable)
Labels cache-bypass memory	53.0 B/op	53.0 B/op	0.0% (stable)
Labels cache-bypass allocations	3.0 allocs/op	3.0 allocs/op	0.0% (stable)
High-concurrency throughput	129740.0 req/s	122980.0 req/s	-5.2% (stable)
High-concurrency memory growth	0.4 MB	0.4 MB	0.0% (stable)

State

• Coverage, compatibility, and sampled performance are reported here from the same PR workflow.
• This is a delta report, not a release gate by itself. Required checks still decide merge safety.
• Performance is a smoke comparison, not a full benchmark lab run.
• Delta states use the same noise guards as the quality gate (percent + absolute + low-baseline checks), so report labels match merge-gate behavior.