feat(image): display formatted pull progress on Windows terminals

[mdelapenya]

Summary

• Fixes image pull progress display on Windows terminals (e.g., PowerShell)
• Adds DisplayProgress() helper for consumers to use formatted progress
• Changes default pull handler to use jsonmessage.DisplayJSONMessagesStream() for proper formatting
• Consistent with how the SDK already handles image build progress

Problem

Prior to this fix, image pull progress displays incorrectly on Windows terminals, showing raw JSON instead of formatted progress bars:
{"status":"Downloading","progressDetail":{"current":1048576,"total":89933544},"progress":"[> ] 1.049MB/89.93MB","id":"67ca873efd04"}

Solution

With this fix, pull progress is properly displayed:
nginx: Pulling from library/nginx
abc123: Pull complete
Digest: sha256:...
Status: Downloaded newer image

Public API Addition

Consumers can now use the DisplayProgress() helper to get formatted progress with custom writers:

// Display to stderr
err := image.Pull(ctx, "nginx:latest",
    image.WithPullHandler(image.DisplayProgress(os.Stderr)))

// Display to custom writer
var buf bytes.Buffer
err := image.Pull(ctx, "nginx:latest",
    image.WithPullHandler(image.DisplayProgress(&buf)))

Changes

• image/pull.go: Add DisplayProgress() helper and use jsonmessage.DisplayJSONMessagesStream()
• image/mocks_test.go: Update mock to return JSON messages for testing
• image/pull_examples_test.go: Add example showing DisplayProgress() usage

Related

• Benefits all SDK consumers
• Provides reusable helper for custom progress display

Test Plan

• Code builds successfully
• Code passes go vet
• Formatted with go fmt
• Consistent with existing build progress implementation
• Public API documented with example

🤖 Generated with https://claude.com/claude-code

[Copilot]

Pull Request Overview

This PR enhances the Docker image pull functionality by adding formatted progress output using Docker's jsonmessage package. The changes enable automatic terminal detection for colored progress bars and properly formatted JSON message display.

Key changes:

• Added a new DisplayProgress function that creates a pull handler with formatted progress output
• Modified defaultPullHandler to use DisplayProgress(os.Stdout) instead of silently consuming the pull stream
• Updated mock test data to return realistic JSON-formatted Docker pull output

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
image/pull.go	Added DisplayProgress function and updated defaultPullHandler to display formatted progress
image/pull_examples_test.go	Added example demonstrating usage of DisplayProgress function
image/mocks_test.go	Updated mock pull output to return JSON-formatted messages for realistic testing

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[mdelapenya]

As described in db36efb 's commit message, the performance degradation is expected, so we accept this trade-off

[ctalledo]

Thanks for this change, LGTM.

Just one question on a test.