refactor: use b.Loop() to simplify the code and improve performance

[rustversion]

These changes use b.Loop() to simplify the code and improve performance
Supported by Go Team, more info: https://go.dev/blog/testing-b-loop

Before:

 go test -run=^$ -bench=. ./util/base58                   
goos: darwin
goarch: arm64
pkg: github.com/MixinNetwork/mixin/util/base58
cpu: Apple M4
BenchmarkBase58Encode_5K-10      	    1257	    958575 ns/op	   5.22 MB/s
BenchmarkBase58Encode_100K-10    	       3	 377777069 ns/op	   0.26 MB/s
BenchmarkBase58Decode_5K-10      	   13212	     91630 ns/op	  74.53 MB/s
BenchmarkBase58Decode_100K-10    	      42	  28674206 ns/op	   4.76 MB/s
PASS
ok  	github.com/MixinNetwork/mixin/util/base58	8.076s

After:

go test -run=^$ -bench=. ./util/base58   
goos: darwin
goarch: arm64
pkg: github.com/MixinNetwork/mixin/util/base58
cpu: Apple M4
BenchmarkBase58Encode_5K-10      	    1269	    945163 ns/op	   5.29 MB/s
BenchmarkBase58Encode_100K-10    	       3	 378859333 ns/op	   0.26 MB/s
BenchmarkBase58Decode_5K-10      	   13183	     91083 ns/op	  74.98 MB/s
BenchmarkBase58Decode_100K-10    	      40	  28572274 ns/op	   4.78 MB/s
PASS
ok  	github.com/MixinNetwork/mixin/util/base58	5.387s