decode to string instead of uint

[hayesZach]

Note

Low Risk
Low risk: scoped to CSFloat ingestion pagination, only changes JSON decoding/parsing of next_cursor and returns an error if the cursor is not numeric.

Overview
Updates the CSFloat ingestor to decode next_cursor as a string (matching the upstream API) and then parse it into a uint for internal pagination.

Adds explicit cursor parsing/error handling and keeps the rest of the sync flow unchanged.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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