feat: unnest transform

[close2]

fixes #77

[Copilot]

Pull request overview

This PR addresses issue #77 by changing the library’s stream transformation model so CSV decoding/encoding streams emit one row per event, eliminating the extra List<List<...>> nesting that appeared when using Stream.transform(...).toList() after upgrading to v7.

Changes:

• Refactors CsvDecoder and CsvEncoder to be StreamTransformerBase implementations (row-per-event) while keeping batch convert(...)-style APIs.
• Introduces Csv as the primary API (with deprecated CsvCodec typedef) and adds asCodec() as a dart:convert Codec adapter for .fuse() use cases.
• Updates tests, examples, benchmarks, docs, changelog, and bumps package version to 8.0.0.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/src/csv_decoder.dart	Refactors decoding to emit one row per stream event while preserving batch decode via convert().
lib/src/csv_encoder.dart	Refactors encoding to accept one row per stream event and preserves batch encode via convert().
lib/src/csv_codec.dart	Replaces CsvCodec class with Csv, adds encode/decode helpers and introduces asCodec() adapter.
lib/csv.dart	Updates top-level csv/excel instances to use Csv.
test/csv_test.dart	Updates chunked conversion tests to assert flat row emission and new encoder input types.
test/small_chunk_test.dart	Updates expectations to match row-per-event decoding (no manual flattening).
test/parse_headers_test.dart	Updates to construct Csv(parseHeaders: true) and keeps header parsing behavior tests.
test/split_escape_test.dart	Updates chunked decoding sink setup to collect row events directly.
test/split_crlf_test.dart	Same as above for CRLF chunking scenarios.
test/multi_char_delim_test.dart	Same as above for multi-character delimiter chunking scenarios.
example/csv_fuse_example.dart	Updates .fuse() example to use csv.asCodec() as the supported path.
benchmark/benchmark_csv.dart	Updates benchmark streams to use per-row events and uses asCodec() for fuse benchmarking.
README.md	Documents v8 upgrade, stream row-per-event behavior, and explains the Codec/asCodec() tradeoff.
CHANGELOG.md	Adds v8.0.0 entry describing the fix and breaking changes.
pubspec.yaml	Bumps version to 8.0.0 and updates package description.

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