Return early in semconv generated packages if no attributes passed (#7222)

- Reduces unnecessary allocations for empty attribute
- Fixes case where we were double recording for `Record` methods

Author: MrAlias

semconv/templates/registry/go/instrument.j2

@@ -115,6 +115,11 @@ func (m {{ name }}) Add(
 	incr {{ value_type(metric) | lower }},
 {{ params(metric.attributes, pkg=pkg, prefix="\t") }}
 ) {
+	if len(attrs) == 0 {
+		m.{{ inst }}.Add(ctx, incr)
+		return
+	}
+
 	o := addOptPool.Get().(*[]metric.AddOption)
 	defer func() {
 		*o = (*o)[:0]
@@ -171,6 +176,11 @@ func (m {{ name }}) Record(
 	val {{ value_type(metric) | lower }},
 {{ params(metric.attributes, pkg=pkg, prefix="\t") }}
 ) {
+	if len(attrs) == 0 {
+		m.{{ inst }}.Record(ctx, val)
+		return
+	}
+
 	o := recOptPool.Get().(*[]metric.RecordOption)
 	defer func() {
 		*o = (*o)[:0]
@@ -205,6 +215,7 @@ func (m {{ name }}) Record(
 func (m {{ name }}) Record(ctx context.Context, val {{ value_type(metric) | lower }}, attrs ...attribute.KeyValue) {
 	if len(attrs) == 0 {
 		m.{{ inst }}.Record(ctx, val)
+		return
 	}
 
 	o := recOptPool.Get().(*[]metric.RecordOption)