New async client

[mewwts]

Note

Refactors the async client with built-in retry/backoff and context-managed sessions, adds pagination/CSV utilities, enforces sampling validation, raises HTTP errors for JSON responses, and updates/expands tests.

• Async Client:
  • Introduces _request with exponential backoff on 429/5xx and ClientError; configurable attempts/statuses.
  • Enforces context-managed sessions (__aenter__/__aexit__), refactors connect/disconnect, and uses default SSL; removes certifi and custom retry exceptions.
  • Updates routing (_route_url) and adds _require_session.
  • Adds _collect_pages pagination helper and _validate_sampling.
  • Improves CSV handling: parse x-dune-next-* headers, cast next_offset to int, read to BytesIO, and release responses.
  • Refresh loop uses terminal states and raises QueryFailedError on failure.
• Base/Sync:
  • Always call response.raise_for_status() even for JSON responses.
• Tests:
  • Adds unit tests for pagination, validation, terminal states, CSV parsing, and retry/backoff.
  • E2E tweaks: _session set to None after disconnect; error-path assertions expect HTTPError with status codes.

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[mewwts]

@cursor review

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[bh2smith]

Looks alright. I suppose the tests give a pretty good indication that users won't have to change their code on update.