Fixer mixer

[crStiv]

Closes: No specific issue number.

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This PR:

• Fixes multiple typos and minor wording inconsistencies in the documentation for asynchronous data retrieval.
• Updates the SQL migration file to correct a typographical error in comments.

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This PR does not:

• Introduce new functionality or features.
• Modify any core logic or add significant changes to the repository.

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Key places to review:

• doc/async-retrieval.md:
  • Corrected redundant word usage, e.g., "best effort" to "best-effort."
  • Adjusted grammar for clarity in multiple sections, e.g., “effect” changed to “affect” and “need” corrected to “needed.”
  • Updated phrasing for better readability, e.g., "increment sequentially" instead of "an increment sequentially."
• migrations/postgres/V100__drop_leaf_payload.sql:
  • Typo fix in comment: “unnecesssary” corrected to “unnecessary.”

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How to test this PR:

No specific tests are required as changes are limited to documentation and comments. Review for accuracy and clarity.

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Complete the following items before merging:

• Verify that the documentation edits align with intended meaning.
• Confirm that the SQL migration file comment changes are accurate and maintain readability.

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Allow edits by maintainers.