Revert "[perf] Skip cache check if store path exists locally" (#2054)

Reverts #2042

#2042 introduced a bug where adding non-cached packages
would fail to add them to the flake on the first attempt. (it would
succeed on subsequent attempts after the package is already in the
store).

The root cause is that `fetchNarInfoStatus` gets called twice per
package (even though we cache it and we're not supposed to call it
twice). The first call returns `false` because the package is not
cached. The second call returns `true` because the package is already in
store. This discrepancy essentially causes the package not to appear on
the flake at all. When updating state again, the package is already in
the nix store so both `fetchNarInfoStatus` calls return true.

I think reverting this is best immediate course of action. In follow up
we should fix `fetchNarInfoStatus` so it only gets called once (it will
improve performance and is more correct).

Later on we can think of better way to do #2042. The
current implementation is a bit fragile and not 100% consistent with the
initial intention of the function, so I'm concerned it can lead to more
bugs in the future.

internal/devpkg/narinfo_cache.go

@@ -5,13 +5,11 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"os"
 	"sync"
 	"time"
 
 	"github.com/pkg/errors"
 	"go.jetpack.io/devbox/internal/boxcli/featureflag"
-	"go.jetpack.io/devbox/internal/debug"
 	"go.jetpack.io/devbox/internal/lock"
 	"go.jetpack.io/devbox/internal/nix"
 	"golang.org/x/sync/errgroup"
@@ -53,7 +51,6 @@ func (p *Package) IsInBinaryCache() (bool, error) {
 // package in the list, and caches the result.
 // Callers of IsInBinaryCache may call this function first as a perf-optimization.
 func FillNarInfoCache(ctx context.Context, packages ...*Package) error {
-	defer debug.FunctionTimer().End()
 	if !featureflag.RemoveNixpkgs.Enabled() {
 		return nil
 	}
@@ -148,11 +145,6 @@ func (p *Package) fetchNarInfoStatus(outputName string) (bool, error) {
 
 	outputInCache := map[string]bool{} // key = output name, value = in cache
 	for _, output := range outputs {
-		// if store path exists locally, then it is equivalent to being in the cache.
-		if _, err := os.Stat(output.Path); err == nil {
-			outputInCache[output.Name] = true
-			continue
-		}
 		pathParts := nix.NewStorePathParts(output.Path)
 		reqURL := BinaryCache + "/" + pathParts.Hash + ".narinfo"
 		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)