Replace retrieval synonyms with glossary terms

[thodson-usgs]

Parent

#406

What to build

Replace unsupported alternate spellings of the package's core retrieval terms after the parallel_chunks explanation has been settled. Where "sub-request" denotes one piece of a split query, use chunk; where concurrency is described, use chunks in flight. Where "parallelism" denotes concurrent chunk execution, use fan-out.

Apply the correction across package prose, user documentation, examples, notebooks, comments, and wording-sensitive test messages. Preserve ordinary uses that are not synonyms, references in accepted decisions explaining rejected names, and the independent-item meaning of batch.

Acceptance criteria

• "Sub-request" no longer denotes a chunk anywhere in tracked package, documentation, examples, notebooks, or tests.
• Concurrency descriptions consistently use chunks in flight.
• Uses of "parallelism" that denote concurrent chunk execution are rewritten as fan-out.
• Accepted-decision references to rejected names and ordinary behavioral uses remain unchanged.
• Batch terminology for independent-item skip policy remains unchanged.
• No public identifier, parameter, environment variable, signature, or runtime behavior changes.
• Repository-wide searches demonstrate that every remaining occurrence is an explicit exclusion rather than unresolved drift.
• Notebooks and documentation build successfully, and the offline suite, lint, type checker, and architecture checks pass.

Blocked by

• Describe parallel_chunks as chunk planning #412