High CPU from append: frequent runtime.growslice due to missing slice preallocation

[danidr7]

Describe the bug

• The Append built-in uses excessive CPU due to frequent runtime.growslice calls.

Steps to reproduce

1. Run an INSERT that writes a large number of rows.
2. This triggers multiple append operations that allocate new underlying arrays because the current slice has no predefined capacity.
3. Capture a Go CPU profile and inspect the hot spots for append and runtime.growslice.

Expected behavior

• Provide a way to preallocate slice capacity (or otherwise reduce allocations) so that calls to runtime.growslice are minimized or eliminated.

Code example

• The current column type does not allow setting the initial capacity of the slice:

type ColDateTime64 struct {
    Data         []DateTime64
    Location     *time.Location
    Precision    Precision
    PrecisionSet bool
}

[earwin]

You can reuse proto.Input (and columns it contains) between blocks/inserts by calling Reset(), works like a charm.