Predicate still has cast when comparing Timestamp(Nano, None) to a timestamp literal, so can't be pushed down or used for pruning

[alamb]

Describe the bug
Comparing a Timestamp(Nanosecond, None) column to a timestamp literal is important for IOx and can be used to potentially prune significant amounts of data and pushed down to scans.

Specifically, to get the last hours of data you can use a predicate like:

col_ts_nano_none < (now() - interval '1 hour')";

Which should be evaluated to something like

test.col_ts_nano_none < TimestampNanosecond(1666612093000000000, Some(\"UTC\")

However, today DataFusion can't get rid of the cast:

CAST(test.col_ts_nano_none AS Timestamp(Nanosecond, Some(\"UTC\"))) < TimestampNanosecond(1666612093000000000, Some(\"UTC\")

To Reproduce
Add this test to the optimizer-integration test:

#[test]
fn timestamp_nano_ts_none_predicates() -> Result<()> {
    let sql = "SELECT col_int32
        FROM test
        WHERE col_ts_nano_none < (now() - interval '1 hour')";
    let plan = test_sql(sql)?;
    // a scan should have the now()... predicate folded to a single
    // constant and compared to the column without a cast so it can be
    // pushed down / pruned
    let expected = "Projection: test.col_int32\n  Filter: test.col_ts_nano_utc < TimestampNanosecond(1666612093000000000, Some(\"UTC\"))\
                    \n    TableScan: test projection=[col_int32, col_ts_nano_none]";
    assert_eq!(expected, format!("{:?}", plan));
    Ok(())
}

It will fail like:

---- timestamp_nano_ts_none_predicates stdout ----
thread 'timestamp_nano_ts_none_predicates' panicked at 'assertion failed: `(left == right)`
  left: `"Projection: test.col_int32\n  Filter: test.col_ts_nano_utc < TimestampNanosecond(1666612093000000000, Some(\"UTC\"))\n    TableScan: test projection=[col_int32, col_ts_nano_none]"`,
 right: `"Projection: test.col_int32\n  Filter: CAST(test.col_ts_nano_none AS Timestamp(Nanosecond, Some(\"UTC\"))) < TimestampNanosecond(1666612093000000000, Some(\"UTC\"))\n    TableScan: test projection=[col_int32, col_ts_nano_none]"`', datafusion/optimizer/tests/integration-test.rs:242:5
stack backtrace:

Because the predicate still contains the cast

 CAST(test.col_ts_nano_none AS Timestamp(Nanosecond, Some(\"UTC\"))) < TimestampNanosecond(1666612093000000000, Some(\"UTC\"))

Expected behavior
Test should pass (though the actual timestamp value may need to be adjusted)

Specifically, the filter should be something like:

test.col_ts_nano_utc < TimestampNanosecond(1666612093000000000, Some(\"UTC\"))\

Additional context
See related IOx issue here: https://github.com/influxdata/influxdb_iox/issues/5875

It is not clear to me if the better fix would be to provide Timestamp(Nanos, UTC) rather than Timestamp(Nanos, None) in this case. However, DataFusion could definitely do a better job with unwrapping the cast

[alamb]

It turns out I accidentally marked this as completed when it is still broken