Automatic resource cleanup via using / Symbol.dispose

[bytebrujo]

Problem

Users must call parser.close() manually to release mmap/file handles; forgetting leaks resources (spec §13.1).

Proposal

Implement [Symbol.dispose] (and [Symbol.asyncDispose]) on CSVParser/CSVWriter so they work with using:

using parser = new CSVParser("data.csv");

Acceptance

• using releases handles automatically
• close() still works; double-dispose is safe
• Tests