fix: remove shared state noParserHints to avoid data race (grafana#11685

)

**What this PR does / why we need it**:

A data race introduced in grafana#11587 was
caught in the [backport to
k184](grafana#11668). This removes the
shared state of a single global `noParserHints` in favor of creating an
empty `Hint` object for each label builder, since the `Hints` is keeping
state of `extracted` and `requiredLabels`.

pkg/logql/log/labels.go

@@ -157,7 +157,7 @@ type LabelsBuilder struct {
 // NewBaseLabelsBuilderWithGrouping creates a new base labels builder with grouping to compute results.
 func NewBaseLabelsBuilderWithGrouping(groups []string, parserKeyHints ParserHint, without, noLabels bool) *BaseLabelsBuilder {
 	if parserKeyHints == nil {
-		parserKeyHints = noParserHints
+		parserKeyHints = NoParserHints()
 	}
 
 	const labelsCapacity = 16
@@ -179,7 +179,7 @@ func NewBaseLabelsBuilderWithGrouping(groups []string, parserKeyHints ParserHint
 
 // NewBaseLabelsBuilder creates a new base labels builder.
 func NewBaseLabelsBuilder() *BaseLabelsBuilder {
-	return NewBaseLabelsBuilderWithGrouping(nil, noParserHints, false, false)
+	return NewBaseLabelsBuilderWithGrouping(nil, NoParserHints(), false, false)
 }
 
 // ForLabels creates a labels builder for a given labels set as base.

pkg/logql/log/parser_hints.go

@@ -6,7 +6,9 @@ import (
 	"github.com/grafana/loki/pkg/logqlmodel"
 )
 
-var noParserHints = &Hints{}
+func NoParserHints() ParserHint {
+	return &Hints{}
+}
 
 // ParserHint are hints given to LogQL parsers.
 // This is specially useful for parser that extract implicitly all possible label keys.