* Optimize (m ModuleInstance) String()
Optimize (m ModuleInstance) String() to preallocate the buffer and use strings.Builder instead of bytes.Buffer
This leads to a common case only doing a single allocation as opposed to a few allocations which the bytes.Buffer is doing.
* adding a benchmark test
Result:
```
$ go test -bench=String ./addrs -benchmem
BenchmarkStringShort-12 18271692 56.52 ns/op 16 B/op 1 allocs/op
BenchmarkStringLong-12 8057071 158.5 ns/op 96 B/op 1 allocs/op
PASS
$ git checkout main addrs/module_instance.go
$ go test -bench=String ./addrs -benchmem
BenchmarkStringShort-12 7690818 162.0 ns/op 80 B/op 2 allocs/op
BenchmarkStringLong-12 2922117 414.1 ns/op 288 B/op 3 allocs/op
```
* Update module_instance_test.go
switch spaces to tabs
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