chore(perf): 25% encoding performance improvement

[reecepbcups]

Summary

goos: linux
goarch: amd64
pkg: github.com/cosmos/iavl
cpu: 13th Gen Intel(R) Core(TM) i9-13900K

Benchmark	Original	Current	Change
BenchmarkNode_encodedSize	5.022 ns	3.748 ns	~25% faster
BenchmarkExport	5.21 ms	5.11 ms	~2% faster
BenchmarkImport	10.41 ms	10.30 ms	~1% faster
BenchmarkImportBatch	208.3 ms	204.5 ms	~2% faster
BenchmarkNode_WriteBytes	128.6 ns	126.5 ns	~1.6% faster
BenchmarkNodeKey	3.724 ns	3.684 ns	~1% faster
BenchmarkTreeString (memory)	17.6 MB	16.6 MB	~6% less
BenchmarkTreeString (allocs)	259,829	249,832	~10,000 fewer