docs: fix duplicate 'of' in pagination docstrings

[chenlichao]

Summary

• Removed a duplicated "of" in the Returns: docstrings of the sync and async list() methods across three resource namespaces (Collections, Models, Predictions).

Change

• replicate/collection.py: "A page of of model collections." → "A page of model collections." (×2)
• replicate/model.py: "A page of of models." → "A page of models." (×2)
• replicate/prediction.py: "A page of of predictions." → "A page of predictions." (×2)

Why this helps

• Fixes a clear documentation typo in the docstrings surfaced by help()/IDE tooling.
• Intentionally documentation-only, tiny (6 lines changed, all comment/docstring text).

Test Plan

• python3 -m py_compile replicate/collection.py replicate/model.py replicate/prediction.py passes
• git diff --check clean
• grep -rn "page of of" replicate/ returns no matches
• Commit signed off (Signed-off-by) per CONTRIBUTING.md