feat: add with_new_children implementations for several nodes

[westonpace]

Some of these nodes don't have children (and so I think we thought with_new_children wouldn't be called on them). Others were simply missing an implementation.

These missing impls are causing errors when trying to use lance as a table provider in lancedb.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 44 lines in your changes missing coverage. Please review.

Project coverage is 78.70%. Comparing base (c69a5a2) to head (b74d3f4).

Files with missing lines	Patch %	Lines
rust/lance/src/io/exec/scalar_index.rs	0.00%	22 Missing ⚠️
rust/lance/src/io/exec/rowids.rs	0.00%	10 Missing ⚠️
rust/lance/src/io/exec/knn.rs	0.00%	6 Missing ⚠️
rust/lance/src/io/exec/pushdown_scan.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3471      +/-   ##
==========================================
- Coverage   78.72%   78.70%   -0.02%     
==========================================
  Files         251      251              
  Lines       92983    93018      +35     
  Branches    92983    93018      +35     
==========================================
+ Hits        73198    73211      +13     
- Misses      16811    16830      +19     
- Partials     2974     2977       +3     

Flag	Coverage Δ
unittests	78.70% <0.00%> (-0.02%)	⬇️

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