feat: add getMeta() for parse metadata output

[bytebrujo]

Summary

• Adds CSVMeta interface with PapaParse-compatible metadata fields
• Adds getMeta() method on CSVParser returning: delimiter, linebreak, aborted, truncated, fields, elapsedMs
• Available before and after iteration
• fields returns a copy of the header names array (or null without headers)
• Exported CSVMeta type from package

Test plan

• Returns correct delimiter (default and custom)
• Returns linebreak
• Returns fields array with header names
• Returns null fields without headers
• aborted is false by default
• truncated is false by default
• elapsedMs is a positive number after parsing
• fields is a copy, not a reference
• Meta available before iteration
• All 38 unit tests pass

Closes #14

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