remove schema in aggs

[PSeitz]

• switch to ColumnType, move tests
• remove Schema dependency in agg

remove schema dependency in preparation to support aggregation on JSON fields

[codecov-commenter]

Codecov Report

Merging #1888 (0248928) into main (e2aa5af) will decrease coverage by 0.03%.
The diff coverage is 99.90%.

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@@            Coverage Diff             @@
##             main    #1888      +/-   ##
==========================================
- Coverage   94.64%   94.62%   -0.03%     
==========================================
  Files         301      302       +1     
  Lines       54924    54918       -6     
==========================================
- Hits        51985    51967      -18     
- Misses       2939     2951      +12     

Impacted Files	Coverage Δ
src/aggregation/mod.rs	93.68% <90.90%> (-4.59%)	⬇️
columnar/src/columnar/column_type.rs	81.33% <100.00%> (ø)
src/aggregation/agg_req_with_accessor.rs	98.05% <100.00%> (-0.16%)	⬇️
src/aggregation/agg_result.rs	73.77% <100.00%> (-1.23%)	⬇️
src/aggregation/agg_tests.rs	100.00% <100.00%> (ø)
src/aggregation/bucket/histogram/histogram.rs	99.55% <100.00%> (-0.01%)	⬇️
src/aggregation/bucket/range.rs	97.49% <100.00%> (+0.02%)	⬆️
src/aggregation/collector.rs	96.62% <100.00%> (-0.04%)	⬇️
src/aggregation/intermediate_agg_result.rs	97.69% <100.00%> (+<0.01%)	⬆️
src/aggregation/metric/mod.rs	94.23% <100.00%> (ø)
... and 6 more

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