[CHORE] Refactor local hash joins + pipeline connections

[colin-ho]

1. Separate hash join into build sink + probe op.
2. Pipeline nodes now return a Pipeline Channel instead of nothing.
3. Put stats counting in the counting senders / receivers.

[codspeed-hq]

CodSpeed Performance Report

Merging #2719 will improve performances by 51.6%

_{Comparing colin/separate-hash-joins (7c76de2) with main (dee1af8)}

Summary

⚡ 1 improvements
✅ 15 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	colin/separate-hash-joins	Change
⚡	test_count[1 Small File]	20.5 ms	13.6 ms	+51.6%

[colin-ho]

No need to chunk in source anymore, since ops do their own buffering.

[samster25]

I think this api can also be Option<&mut dyn IntermediateOperatorState> instead of the Box of one

[colin-ho]

I tried, but had a bit of difficulty. I believe this is because performing a as_deref_mut on Option<Box<dyn IntermediateOperatorState>> returns Option<&mut dyn IntermediateOperatorState + 'static>>, which outlives the original Option<Box<dyn IntermediateOperatorState>>. https://users.rust-lang.org/t/whats-the-lifetime-of-the-output-of-as-deref-mut-of-option-box-dyn-trait/105002/2