[C++][Parquet] Api inconsistency for bpacking32/bpacking64

[emkornfield]

Describe the enhancement requested

unpack32 takes int32* but unpack64 takes int8_t*. I think the unpack64 is correct since we can't rely on alignment and under the hood unpack32 does SafeLoad to avoid ubsan already. We should probably clean this up to make this clearer.

Component(s)

C++, Parquet

[github-actions]

This issue has been marked as stale because it has had no activity in the past 365 days. Please remove the stale label or comment below, or this issue will be closed in 14 days. If this improvement is still desired but has no current owner, please add the 'Status: needs champion' label.

[thisisnic]

This issue has been closed because there has been no activity for the 14 days since the stale warning. Feel free to reopen if this has been closed in error.