Fix leaking slice capacity #140

Benchdiff Results

Benchmark Command: go test ./... -run ^ -bench . -count 5 -benchtime 100ms -cpu 1,2 -benchmem

HEAD sha: b197d63

Base sha: c584875

Degraded: false

pkg: github.com/elastic/apm-data/codec
goos: linux
goarch: amd64

name	old time/op (ns/op)	±	new time/op (ns/op)	±	delta	±
Encode/format=json	24984.4	1%	25159.4	0%	+0.70%	(p=0.016 n=5+5)
Encode/format=json-2	13119.2	0%	13019.8	1%	~	(p=0.343 n=4+4)
Encode/format=vtproto	4814.6	0%	4798.2	0%	~	(p=0.056 n=5+5)
Encode/format=vtproto-2	2602.4	1%	2591.6	1%	~	(p=0.286 n=5+5)
Decode/format=json	122697	1%	122322	1%	~	(p=0.690 n=5+5)
Decode/format=json-2	64774.2	1%	64831.6	1%	~	(p=0.905 n=4+5)
Decode/format=vtproto	18455.8	6%	17609.4	0%	-4.59%	(p=0.008 n=5+5)
Decode/format=vtproto-2	11299.8	25%	10338.2	1%	~	(p=0.095 n=5+5)

name	old bytes/op (bytes/op)	±	new bytes/op (bytes/op)	±	delta	±
Encode/format=json	6564	0%	6564	0%	~	(all equal)
Encode/format=json-2	6564	0%	6564	0%	~	(all equal)
Encode/format=vtproto	2775	0%	2775	0%	~	(all equal)
Encode/format=vtproto-2	2775	0%	2775	0%	~	(all equal)

name	old alloc/op (B/op)	±	new alloc/op (B/op)	±	delta	±
Encode/format=json	7592	0%	7592	0%	~	(all equal)
Encode/format=json-2	7593	0%	7593	0%	~	(all equal)
Encode/format=vtproto	3072	0%	3072	0%	~	(all equal)
Encode/format=vtproto-2	3072	0%	3072	0%	~	(all equal)
Decode/format=json	14282.2	0%	14282.2	0%	~	(p=1.000 n=5+5)
Decode/format=json-2	14280.8	0%	14282	0%	~	(p=0.079 n=5+4)
Decode/format=vtproto	12952	0%	12952	0%	~	(all equal)
Decode/format=vtproto-2	12952	0%	12952	0%	~	(all equal)

name	old allocs/op (allocs/op)	±	new allocs/op (allocs/op)	±	delta	±
Encode/format=json	26	0%	26	0%	~	(all equal)
Encode/format=json-2	26	0%	26	0%	~	(all equal)
Encode/format=vtproto	1	0%	1	0%	~	(all equal)
Encode/format=vtproto-2	1	0%	1	0%	~	(all equal)
Decode/format=json	379	0%	379	0%	~	(all equal)
Decode/format=json-2	379	0%	379	0%	~	(all equal)
Decode/format=vtproto	348	0%	348	0%	~	(all equal)
Decode/format=vtproto-2	348	0%	348	0%	~	(all equal)

pkg: github.com/elastic/apm-data/input/elasticapm/internal/decoder
goos: linux
goarch: amd64

name	old time/op (ns/op)	±	new time/op (ns/op)	±	delta	±
NDStreamDecoder	276.7	4%	279.06	4%	~	(p=0.151 n=5+5)
NDStreamDecoder-2	148.68	5%	145.85	0%	~	(p=0.556 n=5+4)

name	old alloc/op (B/op)	±	new alloc/op (B/op)	±	delta	±
NDStreamDecoder	72	0%	72	0%	~	(all equal)
NDStreamDecoder-2	72	0%	72	0%	~	(all equal)

name	old allocs/op (allocs/op)	±	new allocs/op (allocs/op)	±	delta	±
NDStreamDecoder	4	0%	4	0%	~	(all equal)
NDStreamDecoder-2	4	0%	4	0%	~	(all equal)

pkg: github.com/elastic/apm-data/model/modeljson
goos: linux
goarch: amd64

name	old time/op (ns/op)	±	new time/op (ns/op)	±	delta	±
APMEventToJSON/to-json	15141.2	4%	15076.2	9%	~	(p=0.548 n=5+5)
APMEventToJSON/to-json-2	12514.8	3%	12513	0%	~	(p=0.889 n=5+5)

name	old alloc/op (B/op)	±	new alloc/op (B/op)	±	delta	±
APMEventToJSON/to-json	2616	0%	2616	0%	~	(all equal)
APMEventToJSON/to-json-2	2616	0%	2616	0%	~	(all equal)

name	old allocs/op (allocs/op)	±	new allocs/op (allocs/op)	±	delta	±
APMEventToJSON/to-json	38	0%	38	0%	~	(all equal)
APMEventToJSON/to-json-2	38	0%	38	0%	~	(all equal)