feat: move fsl handling to structural encodings and add support for miniblock

[westonpace]

Previously we had some support for FSL in the full zip encoder by treating FSL as a "compression". Implementing this the same way in miniblock was rather tricky and it seemed more correct to handle FSL at the structural layer.

Now the structural encoding flattens data and the compression layer just sees a larger array of items and is unaware of any FSL. We may need to revisit this decision in the future if we want to add a "vector compression" algorithm but, as none exists yet, we can worry about that later.

[westonpace]

Leaving as draft until #3323 merges

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.58252% with 120 lines in your changes missing coverage. Please review.

Project coverage is 78.90%. Comparing base (38a0a92) to head (2da51fe).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
rust/lance-encoding/src/data.rs	15.78%	32 Missing ⚠️
rust/lance-datagen/src/generator.rs	0.00%	22 Missing ⚠️
rust/lance-encoding/src/encoder.rs	72.00%	13 Missing and 1 partial ⚠️
.../lance-encoding/src/encodings/logical/primitive.rs	94.52%	7 Missing and 5 partials ⚠️
...ust/lance-encoding/src/encodings/physical/value.rs	0.00%	12 Missing ⚠️
rust/lance-encoding/src/repdef.rs	95.56%	7 Missing and 2 partials ⚠️
rust/lance-encoding/src/format.rs	0.00%	8 Missing ⚠️
rust/lance-io/src/scheduler.rs	25.00%	6 Missing ⚠️
rust/lance-core/src/datatypes.rs	66.66%	2 Missing and 2 partials ⚠️
rust/lance-core/src/utils/path.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3324      +/-   ##
==========================================
- Coverage   78.97%   78.90%   -0.07%     
==========================================
  Files         246      246              
  Lines       87628    88144     +516     
  Branches    87628    88144     +516     
==========================================
+ Hits        69202    69552     +350     
- Misses      15558    15718     +160     
- Partials     2868     2874       +6     

Flag	Coverage Δ
unittests	78.90% <80.58%> (-0.07%)	⬇️

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[wjones127]

Nice work!