Store nulls as densely packed bitfields

[benjaminwinger]

Instead of one value per byte.

I also modified NullMask so that modification is only possible through its functions, not via direct access to the underlying data, so that the mayContainNulls is always set if a non-null bit is copied into the data with NullMask::copyNullMask (which had caused issues since I had missed that requirement initially).

The possibility of values with sizes smaller than one byte breaks a lot of assumptions in the storage logic (a lot of parts rely on the idea of the number of bytes per value), but for this at least the fallout of that isn't too large. In NullNodeColumn I was able to just adjust the numValuesPerPage variable after it has been initially set in NodeColumn to an incorrect value based on the size of each value in bytes, but in ColumnChunk that wasn't possible, since the size is immediately used to create a buffer. Instead I adjusted the value size logic to use bits instead of bytes. It's a little messy right now, but while I'd prefer to keep the null-related specifics inside NullColumnChunk, I imagine that an overhaul of that logic will be necessary anyway once we introduce more complex compression schemes.

A NULL_ logical/physical type was introduced since nulls are now stored differently from bools, but that can be removed again when bools are stored in the same way.

[codecov]

Codecov Report

Patch coverage: 93.60% and project coverage change: -0.04% ⚠️

Comparison is base (924d22e) 89.78% compared to head (2414fe3) 89.75%.
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1862      +/-   ##
==========================================
- Coverage   89.78%   89.75%   -0.04%     
==========================================
  Files         869      869              
  Lines       31050    31155     +105     
==========================================
+ Hits        27878    27962      +84     
- Misses       3172     3193      +21     

Files Changed	Coverage Δ
src/binder/bind/bind_updating_clause.cpp	96.12% <ø> (ø)
src/include/common/types/types.h	100.00% <ø> (ø)
src/include/common/vector/value_vector.h	100.00% <ø> (ø)
...rc/include/storage/storage_structure/lists/lists.h	97.18% <ø> (ø)
src/storage/store/node_column.cpp	78.41% <78.57%> (-0.44%)	⬇️
src/common/null_mask.cpp	94.20% <84.61%> (-5.80%)	⬇️
src/storage/copier/column_chunk.cpp	77.04% <95.83%> (-0.11%)	⬇️
src/common/types/types.cpp	92.92% <100.00%> (+2.75%)	⬆️
src/common/vector/value_vector.cpp	99.47% <100.00%> (+<0.01%)	⬆️
src/include/common/null_mask.h	100.00% <100.00%> (ø)
... and 14 more

... and 16 files with indirect coverage changes

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[ray6080]

Let's have another quick go-over after your changes.