Use encoding/binary to convert hashing seed for better performance (#…

…31660)

**Description:**
I was exploring this processor to better understand how it works and
when reading this function it took me a minute to make sure I understood
that it was converting the seed to LittleEndian ordering. I decided to
see if using the provided `encoding/binary` function would show a
performance improvement and it does. I believe this change improves the
readability of this function as well as improves the performance (albeit
likely in a marginal way for overall performance of this processor)

It also doesn't seem like a changelog entry is needed here given this is
a minor refactor.

**Testing:**
I added a benchmark to show improved performance which I ran locally
with:
`go test -bench="Benchmark*" -run=XXX -benchmem -benchtime=5s -count=10`
Then I compared the previous version to mine using `benchstat`
```
goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/processor/probabilisticsamplerprocessor
         │ old_enc.out  │             new_enc.out              │
         │    sec/op    │    sec/op     vs base                │
32tob-10   2.5105n ± 1%   0.3138n ± 0%  -87.50% (p=0.000 n=10)

         │ old_enc.out │          new_enc.out           │
         │    B/op     │    B/op     vs base            │
32tob-10    0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal

         │ old_enc.out │          new_enc.out           │
         │  allocs/op  │ allocs/op   vs base            │
32tob-10    0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal
```

processor/probabilisticsamplerprocessor/fnvhasher.go

@@ -4,6 +4,7 @@
 package probabilisticsamplerprocessor // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/probabilisticsamplerprocessor"
 
 import (
+	"encoding/binary"
 	"hash/fnv"
 )
 
@@ -19,8 +20,6 @@ func computeHash(b []byte, seed uint32) uint32 {
 // i32tob converts a seed to a byte array to be used as part of fnv.Write()
 func i32tob(val uint32) []byte {
 	r := make([]byte, 4)
-	for i := uint32(0); i < 4; i++ {
-		r[i] = byte((val >> (8 * i)) & 0xff)
-	}
+	binary.LittleEndian.PutUint32(r, val)
 	return r
 }

processor/probabilisticsamplerprocessor/fnvhasher_test.go

@@ -0,0 +1,16 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package probabilisticsamplerprocessor
+
+import (
+	"testing"
+)
+
+func BenchmarkSeedConversion(b *testing.B) {
+	val := uint32(0x3024001) // Just a random 32 bit int
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		i32tob(val)
+	}
+}