internal/rosa: optionally load built-ins from filesystem

This avoids having to rebuild cmd/mbf over and over.

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

internal/rosa/builtins.go

@@ -1,10 +1,13 @@
 package rosa
 
 import (
+	"io/fs"
+	"os"
 	"path"
 	"slices"
 	"strconv"
 	"strings"
+	"time"
 
 	"hakurei.app/internal/pkg"
 )
@@ -115,8 +118,29 @@ func skipGNUTests(tests ...int64) string {
 	return buf.String()
 }
 
-// builtin contains native and embedded [Artifact] registrations.
-var builtin S
+var (
+	// builtin contains native and embedded [Artifact] registrations.
+	builtin S
+
+	// parseTime is the duration of early parsing of built-in azalea expressions.
+	parseTime time.Duration
+)
+
+// ParseTime returns the time taken by early parsing of built-in azalea expressions.
+func ParseTime() time.Duration { return parseTime }
+
+func init() {
+	sub, err := fs.Sub(builtinAzalea, "package")
+	if err != nil {
+		panic(err)
+	}
+	t := time.Now()
+	if err = builtin.RegisterFS(sub); err != nil {
+		println(err.Error())
+		os.Exit(1)
+	}
+	parseTime = time.Since(t)
+}
 
 // New returns the address of a newly populated [S] derived from built-ins.
 func New() *S { return builtin.Clone() }