[processor/deltatocumulativeprocessor] Adjust equal test to not compare functions

[mauri870]

Description

With the collector now on Go 1.23 I'm working on adding iterator support for pdata at open-telemetry/opentelemetry-collector#12380 but the EqualT_test fails when comparing the iterators returned by All.

Since the reflect value of an iter.Seq/iter.Seq2 is reflect.Func, they are not comparable in the usual sense. The go-cmp/cmp is still on Go 1.21 so it does not know about iterators. There is x/exp/xiter.Equal but it is still an open proposal.
See https://go.googlesource.com/go/+/81c66e71d480ae2372b7eea4bcdf600b50fdd5e1/src/reflect/deepequal.go#158.

Examples of the test failures:

expo_test.go:203: Attributes().All(): 0xd1b400 != 0xd1b400
expo_test.go:203: Exemplars().All(): 0xe2be20 != 0xe2be20

This PR adjusts the equal logic to skip the equality check for functions.

Link to tracking issue

For open-telemetry/opentelemetry-collector#12380

[mauri870]

I don't think this needs a changelog entry so I appreciate if a mantainer can add the Skip Changelog label or equivalent.

[sh0rez]

Oh interesting. Looking at this, I think there is little value in comparing returned funcs at all (whether they are iterators or not). how about we skip them altogether?

[mauri870]

how about we skip them altogether?

Fair point, I will do that.

[sh0rez]

@open-telemetry/collector-contrib-approvers this is ready to merge