chore: make syncstore generic

[gsquared94]

This PR makes the util.SyncStore generic. This helps simplify the client code by providing type safety for method parameters and return types, and removes typecasting.

Before:

func (h *artifactHasherImpl) safeHash(ctx context.Context, a *latest.Artifact, platforms platform.Matcher) (string, error) {
	val := h.syncStore.Exec(a.ImageName,
		func() interface{} {
			hash, err := singleArtifactHash(ctx, h.lister, a, h.mode, platforms)
			if err != nil {
				return err
			}
			return hash
		})
	switch t := val.(type) {
	case error:
		return "", t
	case string:
		return t, nil
	default:
		return "", fmt.Errorf("internal error when retrieving cache result of type %T", t)
	}
}

After:

func (h *artifactHasherImpl) safeHash(ctx context.Context, a *latest.Artifact, platforms platform.Matcher) (string, error) {
	return h.syncStore.Exec(a.ImageName,
		func() (string, error) {
			return singleArtifactHash(ctx, h.lister, a, h.mode, platforms)
		})
}

[codecov]

Codecov Report

Merging #8000 (0c34e1f) into main (290280e) will decrease coverage by 3.76%.
The diff coverage is 54.09%.

@@            Coverage Diff             @@
##             main    #8000      +/-   ##
==========================================
- Coverage   70.48%   66.71%   -3.77%     
==========================================
  Files         515      596      +81     
  Lines       23150    28894    +5744     
==========================================
+ Hits        16317    19278    +2961     
- Misses       5776     8194    +2418     
- Partials     1057     1422     +365     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/credits/export.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/deploy.go	40.90% <0.00%> (-12.94%)	⬇️
cmd/skaffold/app/cmd/test.go	44.44% <0.00%> (ø)
cmd/skaffold/app/exitcode.go	100.00% <ø> (+6.66%)	⬆️
cmd/skaffold/skaffold.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/inspect_tests.go	62.50% <14.28%> (-1.14%)	⬇️
cmd/skaffold/app/cmd/render.go	35.48% <18.18%> (-5.90%)	⬇️
cmd/skaffold/app/cmd/lsp.go	28.12% <28.12%> (ø)
cmd/skaffold/app/cmd/run.go	64.28% <33.33%> (-9.63%)	⬇️
cmd/skaffold/app/cmd/fix.go	56.41% <37.50%> (-20.07%)	⬇️
... and 390 more

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