impl Debug for TextureBlitter

[euclio]

Description

Derives Debug for TextureBlitter and its builder. This makes it easier for downstream structures to derive Debug as well.

It might make sense to enable warn(missing_debug_implementations) at the crate level to catch issues like this, but there are some structs that have a non-derivable implementation, and I noticed that there are otherwise no manual Debug implementations in the codebase.

Testing

N/A.

Squash or Rebase?

N/A

Checklist

• I self-reviewed and fully understand this PR.
• WebGPU implementations built with wgpu may be affected behaviorally.
• Validation and feature gates are in place to confine behavioral changes.
• Tests demonstrate the validation and altered logic works.
• CHANGELOG.md entries for the user-facing effects of this change are present.
• The PR is minimal, and doesn't make sense to land as multiple PRs.
• Commits are logically scoped and individually reviewable.
• The PR description has enough context to understand the motivation and solution implemented.

[cwfitzgerald]

Adding missing_debug_implementations seems reasonable, we can manually derive stuff that needs to be manually derived.