docs: auto-build refactored namespace integrations doc

[jackye1995]

Integrations are refactored to repo https://github.com/lance-format/lance-namespace-impls

Will be built to https://lance.org/format/namespace/integrations

[github-actions]

Code Review

P1: Potential Build Failure - Missing Directory

The workflow copies files to docs/src/format/namespace/integrations/ but there's no step that creates this directory:

cp lance-namespace-impls/docs/src/hive2.md docs/src/format/namespace/integrations/

The docs/src/format/namespace/ folder is created by copying from lance-namespace repo, but if that repo doesn't contain an integrations/ subdirectory, the cp commands will fail.

Suggested fix: Add mkdir -p docs/src/format/namespace/integrations before the copy commands:

- name: Copy lance-namespace-impls docs
  run: |
    # Ensure the integrations directory exists
    mkdir -p docs/src/format/namespace/integrations
    
    # Copy implementation specs...

Minor: Ordering Consideration

The "Copy lance-namespace-impls docs" step should run after "Copy lance-namespace docs" since it depends on that directory structure. Currently in the diff it appears after the checkout but before the copy steps, which would fail. Please verify the final ordering in the workflow.

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Otherwise the structure looks good for aggregating docs from the refactored namespace-impls repo.