1. remove phmap for padding rows
2. add SimpleFieldVisitorToScarlarType for short circuit type deducing
3. correct type coercion for conflict types bettween integers
4. improve nullable column performance
5. remove shared_ptr dependancy for DataType use TypeIndex instead
6. Optimization by caching the order of fields (which is almost always the same)
and a quick check to match the next expected field, instead of searching the hash table.
benchmark:
In clickbench data, load performance:
12m36.799s ->7m10.934s about 43% latency reduce
In variant_p2/performance.groovy:
3min44s20 -> 1min15s80 about 66% latency reducy
691f3c5ee7