Apply suggestions from code review

Co-authored-by: Owen Mansel-Chan <62447351+owen-mc@users.noreply.github.com>

go/extractor/diagnostics/diagnostics.go

@@ -570,10 +570,11 @@ func EmitExtractionFailedForProjects(path []string) {
 }
 
 func EmitPrivateRegistryUsed(writer DiagnosticsWriter, configs []string) {
-	lines := []string{}
+	n := len(configs)
+	lines := make([]string, n)
 
 	for i := range configs {
-		lines = append(lines, fmt.Sprintf("* %s", configs[i]))
+		lines[i] = fmt.Sprintf("* %s", configs[i])
 	}
 
 	emitDiagnosticTo(
@@ -582,7 +583,7 @@ func EmitPrivateRegistryUsed(writer DiagnosticsWriter, configs []string) {
 		"Go extraction used private package registries",
 		fmt.Sprintf(
 			"Go was extracted using the following private package registr%s:\n\n%s\n",
-			plural(len(lines), "y", "ies"),
+			plural(n, "y", "ies"),
 			strings.Join(lines, "\n")),
 		severityNote,
 		fullVisibility,

go/extractor/registries/registryproxy.go

@@ -112,7 +112,7 @@ func getEnvVars() []string {
 		if err != nil {
 			slog.Error("Unable to parse proxy configurations", slog.String("error", err.Error()))
 		} else {
-			activeConfigs := []RegistryConfig{}
+			activeConfigs := make([]RegistryConfig, 0, len(val))
 
 			// We only care about private registry configurations that are relevant to Go and
 			// filter others out at this point.