Improvement: use sync.Map instead of sync.RWMutex in POJORegistry about dubbo-go-hessian2 HOT 4 CLOSED

dubbo-go-hessian2 (master) $ go test -bench=. -benchmem -run=none
goos: darwin
goarch: amd64
pkg: github.com/apache/dubbo-go-hessian2
BenchmarkTestRegisterPOJO-4                50000             33158 ns/op           10101 B/op        153 allocs/op
BenchmarkTestEncodeTuple-4                200000             11827 ns/op            2861 B/op         93 allocs/op
BenchmarkTestEncodeDecodeTuple-4           50000             31168 ns/op            8881 B/op        311 allocs/op
BenchmarkEncodeBasePointer-4             1000000              1019 ns/op             608 B/op          7 allocs/op
BenchmarkEncodeDecodeBasePointer-4        500000              4846 ns/op            5320 B/op         28 allocs/op
PASS
ok      github.com/apache/dubbo-go-hessian2     11.994s

dubbo-go-hessian2 (96_sync_map_instead_opt) $ go test -bench=. -benchmem -run=none
goos: darwin
goarch: amd64
pkg: github.com/apache/dubbo-go-hessian2
BenchmarkTestRegisterPOJO-4                50000             47289 ns/op           13143 B/op        267 allocs/op
BenchmarkTestEncodeTuple-4                200000             11227 ns/op            3021 B/op         99 allocs/op
BenchmarkTestEncodeDecodeTuple-4           50000             38296 ns/op            9041 B/op        317 allocs/op
BenchmarkEncodeBasePointer-4             1000000              1516 ns/op             608 B/op          7 allocs/op
BenchmarkEncodeDecodeBasePointer-4        200000              9052 ns/op            5320 B/op         28 allocs/op
PASS
ok      github.com/apache/dubbo-go-hessian2     13.319s