[chore][pkg/stanza] Speed up file deduplication in finder (open-telemetry#34888)

**Description:** <Describe what has changed.>
For large numbers of files, the logic that deduplicates the filenames
between matches is costly. This is mainly due to the O(n^2) deduping
algorithm used. If we instead use a map (as a hashset), we can make this
~O(n).

This PR speeds up the deduplication logic, as well as adds a benchmark
for a case where the filelog receiver is polling many files at once.

**Testing:** <Describe what testing was performed and which tests were
added.>

Running the added benchmark and comparing with benchstat, we can see a
large increase in speed for the large number of files case (10000
monitored files), at the cost of a very slight increase in memory usage:
```
goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/matcher/internal/finder
cpu: Apple M3 Pro
                │    old.txt    │               new.txt               │
                │    sec/op     │    sec/op     vs base               │
Find10kFiles-12   198.636m ± 6%   8.696m ± 16%  -95.62% (p=0.002 n=6)

                │   old.txt    │              new.txt               │
                │     B/op     │     B/op      vs base              │
Find10kFiles-12   5.416Mi ± 0%   5.581Mi ± 0%  +3.04% (p=0.002 n=6)

                │   old.txt   │              new.txt              │
                │  allocs/op  │  allocs/op   vs base              │
Find10kFiles-12   80.06k ± 0%   80.25k ± 0%  +0.23% (p=0.002 n=6)
```

Author: BinaryFissionGames

pkg/stanza/fileconsumer/matcher/internal/finder/finder.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 
 	"github.com/bmatcuk/doublestar/v4"
+	"golang.org/x/exp/maps"
 )
 
 func Validate(globs []string) error {
@@ -23,7 +24,8 @@ func Validate(globs []string) error {
 // FindFiles gets a list of paths given an array of glob patterns to include and exclude
 func FindFiles(includes []string, excludes []string) ([]string, error) {
 	var errs error
-	all := make([]string, 0, len(includes))
+
+	allSet := make(map[string]struct{}, len(includes))
 	for _, include := range includes {
 		matches, err := doublestar.FilepathGlob(include, doublestar.WithFilesOnly(), doublestar.WithFailOnIOErrors())
 		if err != nil {
@@ -40,15 +42,9 @@ func FindFiles(includes []string, excludes []string) ([]string, error) {
 				}
 			}
 
-			for _, existing := range all {
-				if existing == match {
-					continue INCLUDE
-				}
-			}
-
-			all = append(all, match)
+			allSet[match] = struct{}{}
 		}
 	}
 
-	return all, errs
+	return maps.Keys(allSet), errs
 }

pkg/stanza/fileconsumer/matcher/internal/finder/finder_test.go

@@ -4,6 +4,7 @@
 package finder
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -188,7 +189,7 @@ func TestFindFiles(t *testing.T) {
 			}
 			files, err := FindFiles(tc.include, tc.exclude)
 			assert.NoError(t, err)
-			assert.Equal(t, tc.expected, files)
+			assert.ElementsMatch(t, tc.expected, files)
 		})
 	}
 }
@@ -251,7 +252,38 @@ func TestFindFilesWithIOErrors(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			files, err := FindFiles(tc.include, []string{})
 			assert.ErrorContains(t, err, tc.failedMsg)
-			assert.Equal(t, tc.expected, files)
+			assert.ElementsMatch(t, tc.expected, files)
 		})
 	}
 }
+
+// benchResult is package level variable that store the result of the benchmark.
+// It is used to prevent go from optimizing out the benchmarked code.
+var benchResult []string
+
+func BenchmarkFind10kFiles(b *testing.B) {
+	numFiles := 10000
+	tmpDir := b.TempDir()
+
+	// Create a bunch of files for benchmarking
+	for i := range numFiles {
+		path := filepath.Join(tmpDir, fmt.Sprintf("log-%05d.log", i))
+		f, err := os.Create(path)
+		require.NoError(b, err)
+		require.NoError(b, f.Close())
+	}
+
+	includeGlobs := []string{
+		filepath.Join(tmpDir, "log-*.log"),
+	}
+
+	excludeGlobs := []string{}
+
+	var r []string
+	b.ResetTimer()
+	for range b.N {
+		r, _ = FindFiles(includeGlobs, excludeGlobs)
+	}
+
+	benchResult = r
+}

pkg/stanza/fileconsumer/matcher/matcher_test.go

@@ -785,7 +785,7 @@ func TestMatcher(t *testing.T) {
 			} else {
 				assert.NoError(t, err)
 			}
-			assert.Equal(t, tc.expected, files)
+			assert.ElementsMatch(t, tc.expected, files)
 		})
 	}
 }