Re-enable the two ignored CometAggregateSuite metric tests after the DataFusion 55 peak_mem_used change

[andygrove]

Describe the bug

Two tests in CometAggregateSuite are disabled on the DataFusion 55 branch with only a prose TODO and no tracking issue:

// TODO: To be addressed after DF 55 migration
ignore("grouped aggregate metrics are forwarded without fabricating global metrics") {
...
// TODO: To be addressed after DF 55 migration
ignore("range sampling does not report grouped aggregate metrics") {

They assert on spill_count, spilled_bytes, spilled_rows and peak_mem_used. peak_mem_used accounting changed in apache/datafusion#22710, which is what broke them.

Steps to reproduce

Un-ignore either test on the df55 branch.

Expected behavior

Either the assertions are adapted to DataFusion 55's accounting, or the metric is reported the way the tests expect. Either way the skips should point at this issue rather than a prose TODO, which is easy to lose once the branch merges.

Additional context

@sunchao offered to take this as a follow-up after #5262 merges. Related: the CometTPCHQuerySuite off-heap bump tracked separately.

[andygrove]

Tracked under #5709 ([EPIC] DataFusion 55 upgrade follow-ups).