Exporter plugin framework

Build a small plugin framework. The host provides ExporterBase (below). Plugins subclass it and auto-register. Requirements: 1. ExporterBase.__init_subclass__ registers subclasses by their name attribute (nonempty str, unique — duplicates raise ValueError at definition time). 2. Every exporter must implement export(rows) returning a STRING. If a subclass lacks export, raise TypeError at definition time. 3. ExporterBase.create(name) returns an instance or raises KeyError. 4. ExporterBase.names() returns a sorted list of registered names. 5. Provide two built-in plugins: CsvExporter (name='csv', rows of dicts joined as 'k1=v1,k2=v2' with rows on newlines) and JsonLinesExporter (name='jsonl', one compact JSON object per line). 6. Hostile test: registering a plugin named 'csv' again must raise ValueError; a plugin missing export must raise TypeError.

Difficulty: advanced