add some perf log for unsweetenning process, and output IR to file

[mo-xiaoming]

when operating on large variant or record, unsweeten might be slow. Adding some logs when both
- HOBBES_PERF_TRACE_FILE log file path
- HOBBES_PERF_TRACE_THRESHOLD_IN_SECS threshold for unsweetenning on named var

are defined. Logs are in the format of

```
HOBBES_PERF:rexec_data:BEGIN:3:show({a = |A = ()|::|A, B, C|, x = |X = ()|::|X, Y, Z|})
HOBBES_PERF:rexec_data:2:{ a:|A, B, C|, x:|X, Y, Z| }
HOBBES_PERF:rexec_data:3:|X, Y, Z|
HOBBES_PERF:rexec_data:3:|A, B, C|
HOBBES_PERF:rexec_data:END:9
```

```
HOBBES_PERF:rexec_data:BEGIN: 3       :show({a = |A = ()|::|A, B, C|, x = |X = ()|::|X, Y, Z|})
mark           name    mark   duration       expression
```

```
HOBBES_PERF:rexec_data:3                :|X, Y, Z|
mark           name    size_of_variant   variant
```

```
HOBBES_PERF:rexec_data:END   :9
mark           name    mark   new_expressions_generated_by_this_var
```