tp: let INTERVAL INTERSECTION's PER keys be of any one type

[LalitMaganti]

Summary

Lets INTERVAL INTERSECTION's PER keys be of any one type: integers of every width, doubles and strings, not just integers.

Why

PER keys had to be integers, and were widened to Int64 on every batch. Grouping intervals by a name or any other string column was impossible.

Changes

• KeyEncoder (core/exec) lays out each row's keys as bytes with RowLayout, so equal keys have equal bytes and are compared as such. Integers of different widths agree, and nulls agree with each other, as under GROUP BY.
• A key must hold the same type in every operand; otherwise the query fails, naming the key.
• The encoder works out each column's type on the first batch and picks a writer for it. Later batches only check that the columns are shaped as before.
• FlatColumnReader<T>, beside ColumnView, reads a flat column through its selection and validity. INTERVAL INTERSECTION's ts and dur and string keys use it, as does INTERVAL FLATTEN (tp: add INTERVAL FLATTEN to pipelines #7692).
• RowLayout::Slot shrinks to 8 bytes and is passed by value, and rows are written through a new PERFETTO_RESTRICT pointer, so the slot stays in registers while a column is written. The macro is __restrict__ because the macOS SDK defines __restrict away to nothing in C++.

Example

INTERVAL INTERSECTION OF (a AS a, b AS b) PER name
|> SELECT ts, dur, name

Benchmarks

KeyEncoder, against writing keys with a type switch per column on every batch (best of 10, release build):

Benchmark	Before	After	Ratio
BM_KeyEncoderInt64 (2048 rows)	970 ns	708 ns	0.73x
BM_KeyEncoderInt64Nulls (1 in 8 null)	1571 ns	1036 ns	0.66x
BM_KeyEncoderInt64OneRow	6.10 ns	4.26 ns	0.70x

Testing

New key_encoder_unittest.cc, and connection tests for keys of every type, nulls and mismatched types.

[github-actions]

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