fix(analyze): add darwin build tag to all platform-specific files

All files in cmd/analyze/ are macOS-only but several were missing the
//go:build darwin constraint. On Linux (e.g. CodeQL CI), Go compiled
these files without the types defined in main.go (which had the tag),
causing undefined symbol errors for dirEntry, fileEntry, scanResult,
cacheEntry, historyEntry and model.

- Add //go:build darwin to heap.go, cache.go, scanner.go, cleanable.go,
  delete.go, format.go, constants.go and all *_test.go files

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cmd/analyze/main_stub.go

@@ -0,0 +1,13 @@
+//go:build !darwin
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	fmt.Fprintln(os.Stderr, "analyze is only supported on macOS")
+	os.Exit(1)
+}