Use count-based progress for Docker image pulls

[agners]

Proposed change

Refactor Docker image pull progress to use a simpler count-based approach where each layer contributes equally (100% / total_layers) regardless of size.

The core issue was that Docker rate-limits concurrent downloads (by default 3 at a time, see Docker DefaultMaxConcurrentDownloads constant) and reports layer sizes only when downloading starts. With the previous size-weighted progress calculation, large layers appearing late would cause progress to drop dramatically (e.g., 59% -> 29%) as the total size increased. We prevented the progress from going backwards, but in practice that meant the progress would stale for an extended amount of time.

The new approach:

• Each layer contributes equally to overall progress
• Per-layer progress: 70% download weight, 30% extraction weight
• Progress only starts after first "Downloading" event (when full layer count is known)
• Always caps at 99% - job completion handles final 100%

This moves progress tracking to a dedicated module (pull_progress.py) and removes the complex size-based scaling logic that tried to account for unknown layer sizes. With this, there is always some progress. Unfortunately, it also means that progress slows down towards the completion, since the larger layers are then still downloaded/extracted. But this is the best we can do currently.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (which adds functionality to the supervisor)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:
• Link to cli pull request:
• Link to client library pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Ruff (ruff format supervisor tests)
• Tests have been added to verify that the new code works.

If API endpoints or add-on configuration are added/changed:

• Documentation added/updated for developers.home-assistant.io
• CLI updated (if necessary)
• Client library updated (if necessary)