fix(isthmus)!: apply the projection a read relation carries

[alexandrefimov]

AbstractReadRel applies a read's projection when it derives the record type, so the relation produces the columns the mask keeps. The conversion built the scan from the initial schema and gave the Calcite node every column of it, mask or no mask.

An emit mapping selects by index, and so does every field reference a parent relation makes. Both index the columns the relation produces, so against that node they landed on the wrong columns, with no error. A VirtualTableScan carrying a projection was refused outright rather than converted against those columns.

NamedScan t(a i64, b string, c fp64), projection = mask[a, c], emit = [1]
  record type      Struct{[FP64]}          -- column c
  Calcite row type RecordType(VARCHAR b)   -- column b

The mask now becomes a projection above the scan and below the emit mapping, for a named table and a virtual one alike. Converting back gives that projection rather than the mask -- a Project over the whole schema, selecting the same columns in the same order -- so a round trip keeps the record type and not the encoding.

A mask that selects inside a column -- some of a struct's fields, some of a list's elements -- throws UnsupportedOperationException: applying it would mean rebuilding the column's value, which this conversion does not do.

The masked columns come out in the order the mask lists them. Spec v0.102.0 does not settle whether a mask may reorder at all: expressions/field_references.md describes a mask as removing columns and raises reordering as an open question. MaskExpressionTypeProjector already derives the record type in that order, though, and refusing a mask that reorders would reject plans the model accepts.

This addresses the projection part of #1204, which also names filter and best_effort_filter. #1260 applies filter; best_effort_filter is still dropped.

BREAKING CHANGE: a NamedScan carrying a projection now converts to Calcite with the mask applied, where it used to convert with the mask dropped and give a tree whose columns were not the relation's. A VirtualTableScan carrying one converts as well, where it used to be refused. A NamedScan whose mask selects inside a column now throws UnsupportedOperationException, where that projection used to be dropped in silence along with the rest.