feat: add sort_merge_join (#397)

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# Please go through the following checklist
- [x] The PR title and commit messages adhere to guidelines here:
https://github.com/spaceandtimelabs/sxt-proof-of-sql/blob/main/CONTRIBUTING.md.
In particular `!` is used if and only if at least one breaking change
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- The following upstream PRs have been approved and merged:
  - [x] #391 
  - [x] #396


# Rationale for this change
This PR adds the actual sort-merge join process which completes a part
of #394.
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 Add `NestedLoopJoinExec`.
 Closes #345.

Since we added `HashJoinExec` in #323 it has been possible to do
provable inner joins. However performance is not satisfactory in some
cases. Hence we need to fix the problem by implement
`NestedLoopJoinExec` and speed up the code
 for `HashJoinExec`.
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# What changes are included in this PR?
- add `sort_merge_join`.
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- Add `NestedLoopJoinExec`.
- Speed up `HashJoinExec`.
- Route joins to `NestedLoopJoinExec` if the outer input is sufficiently
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# Are these changes tested?
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