Fix the logic to fetch the rows

[severo]

We now allow the estimated row numbers in different random row ranges to overlap. We only reassign them when the bytes are contiguous and we merge two ranges.
The consequence is that the response is a lot faster.

[Copilot]

Pull Request Overview

This PR refactors the CSV row fetching logic to improve performance by allowing row number estimates in different random ranges to overlap. Previously, the system would reassign row numbers across all ranges to prevent overlap, which was slower. Now, row numbers are only reassigned when bytes are contiguous and ranges are merged. The changes also introduce a "prefix rows" fetching strategy to handle partial rows when starting from estimated byte positions.

Key changes:

• Modified CSVCache.store() to require a firstRow parameter for creating new ranges
• Refactored getNextMissingRow() to return separate firstByteToFetch and firstByteToStore values along with expected firstRow
• Reduced default chunk size from 500KB to 100KB for finer-grained fetching when estimating positions

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/cache.ts	Added firstRow parameter to store() method; refactored getNextMissingRow() to support prefix fetching with separate fetch/store byte positions
src/dataframe.ts	Refactored fetch loop to use new getNextMissingRow() API; added prefix row fetching; changed event emission to per-row instead of per-fetch; reduced default chunk size to 100KB
test/cache.test.ts	Updated all store() calls to include required firstRow parameter; updated getNextMissingRow() test expectations for new return structure; removed test for row number estimation across ranges
test/dataframe.test.ts	Added extra row to test data; updated expected values to reflect new fetching behavior with prefix rows
src/Welcome.tsx	Added new example dataset (19th-century novelists) for testing with large files
package.json	Updated dependencies: csv-range to 0.0.10, vitest/coverage to 4.0.12, eslint plugins to latest versions, vite to 7.2.4
package-lock.json	Updated lockfile to match package.json dependency changes

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