Lazy buffer allocation

[scunningham]

Lazily defer writer buffer allocation until necessary. This has two advantages:

1. Less data allocated at init time.
2. Buffers are freed on a block write. This means a Flush will free the writer buffers, which could be useful for an application that writes/flushes in bursts.

Because write blocks are managed by a shared pool, this change should have minimal performance impact.

[Copilot]

Pull Request Overview

This PR implements lazy buffer allocation for both synchronous and asynchronous writers, deferring memory allocation until data needs to be written. This reduces initial memory usage and allows buffers to be freed after block writes/flushes.

Key changes:

• Removed immediate buffer allocation during writer initialization
• Added lazy allocation when buffers are actually needed for writing
• Enhanced state tracking to properly manage closed state

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
internal/pkg/sync/writer.go	Implements lazy buffer allocation and adds explicit closed state tracking
internal/pkg/async/writer.go	Implements lazy buffer allocation with a state flag system for better state management

Comments suppressed due to low confidence (1)

internal/pkg/sync/writer.go:143

• Potential nil pointer dereference. The code returns w.srcBlk to the pool without checking if it's nil first. With lazy allocation, w.srcBlk could be nil if Close() is called before any writes occur.

	blk.ReturnBlk(w.srcBlk)