internal/rosa: track evaluation time

Useful to track performance regressions over migrations.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -10,6 +10,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"time"
 
 	"hakurei.app/fhs"
 	"hakurei.app/internal/pkg"
@@ -612,6 +613,12 @@ var native S
 // Native returns the global [S].
 func Native() *S { return &native }
 
+// evalTime is the duration of the initial built-in evaluation.
+var evalTime time.Duration
+
+// EvalTime returns the duration of the initial built-in evaluation.
+func EvalTime() time.Duration { return evalTime }
+
 // nativeB is the backing directory of built-in azalea-based [Artifact]
 // implementations.
 //
@@ -623,8 +630,10 @@ func init() {
 	if err != nil {
 		panic(err)
 	}
+	t := time.Now()
 	if err = native.EvaluateFS(sub); err != nil {
 		println(err.Error())
 		os.Exit(1)
 	}
+	evalTime = time.Since(t)
 }