feat: add the repetition index to the miniblock write path

[westonpace]

The repetition index is what will give us random access support when we have list data. At a high level it stores the number of top-level rows in each mini-block chunk. We can use this later to figure out which chunks we need to read.

In reality things are a little more complicated because we don't mandate that each chunk starts with a brand new row (e.g. a row can span multiple mini-block chunks). This is useful because we eventually want to support arbitrarily deep nested access. If we create not-so-mini blocks in the presence of large lists then we introduce read amplification we'd like to avoid.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 42.99674% with 175 lines in your changes missing coverage. Please review.

Project coverage is 78.44%. Comparing base (5ff966d) to head (071984b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
rust/lance-encoding/src/encodings/logical/list.rs	10.23%	112 Missing and 2 partials ⚠️
.../lance-encoding/src/encodings/logical/primitive.rs	68.69%	30 Missing and 6 partials ⚠️
rust/lance-encoding/src/encoder.rs	18.18%	8 Missing and 1 partial ⚠️
rust/lance-encoding/src/decoder.rs	0.00%	8 Missing ⚠️
...ust/lance-encoding/src/encodings/logical/struct.rs	72.72%	6 Missing ⚠️
rust/lance-encoding-datafusion/src/zone.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3208      +/-   ##
==========================================
- Coverage   78.55%   78.44%   -0.11%     
==========================================
  Files         244      244              
  Lines       84298    84554     +256     
  Branches    84298    84554     +256     
==========================================
+ Hits        66218    66332     +114     
- Misses      15284    15417     +133     
- Partials     2796     2805       +9     

Flag	Coverage Δ
unittests	78.44% <42.99%> (-0.11%)	⬇️

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