Investigate Reusing FieldError && StructErrors structs

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look into reusing these structs, using channels, to reduce memory allocations even further

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only StructErrors can be reused with the updated code structure

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Old Benchmarks
$ go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkValidateField-4             5000000           333 ns/op          16 B/op          1 allocs/op
BenchmarkValidateStructSimple-4       500000          2597 ns/op         752 B/op         13 allocs/op
BenchmarkTemplateParallelSimple-4    1000000          1138 ns/op         753 B/op         13 allocs/op
BenchmarkValidateStructLarge-4        100000         14663 ns/op        4806 B/op         78 allocs/op
BenchmarkTemplateParallelLarge-4      200000          7112 ns/op        4810 B/op         78 allocs/op

New Benchmarks
$ go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkValidateField-4             5000000           318 ns/op          16 B/op          1 allocs/op
BenchmarkValidateStructSimple-4       500000          2471 ns/op         624 B/op         10 allocs/op
BenchmarkTemplateParallelSimple-4    2000000           975 ns/op         624 B/op         10 allocs/op
BenchmarkValidateStructLarge-4        100000         13979 ns/op        4293 B/op         66 allocs/op
BenchmarkTemplateParallelLarge-4      200000          5947 ns/op        4298 B/op         66 allocs/op