Epic: `ScanPlan` (replacing `LayoutReader`s)

[joseph-isaacs]

This Epic is for tracking the migration from LayoutReader to ScanPlan to new system similar to Arrays for reducing and executing arrays. ScanPlans need compute and I/O and maybe subtasks. For now we will move the reduce rules. This could be seen as a physical plan (ScanPlan) and execution will be executing that plan.

Status

Proposed.

Goal

• Move to Scan from using LayoutReader API to ScanPlan API
• Find and use a new execution system for Scan Plans. This Layout Reader V27 #8954 or something else.

Motivation

• This will give us control of expression/aggregation and other pushdown.
• The changed executor will give us control over resource usage.

Unresolved questions

• None yet.