QuickBook Format Handler (`formats/quickbook.py`)

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Problem

Weblate needs a registered monolingual format so .qbk files can be opened, converted to a translation store, and written back using the same patterns as other ConvertFormat types (for example AsciiDoc). Without a dedicated handler, QuickBook sources cannot participate in the normal Weblate convert workflow.

Acceptance Criteria

• QuickBookFormat subclasses Weblate’s ConvertFormat and declares name, autoload patterns (*.qbk), format_id, and monolingual.
• convertfile builds a store from uploaded .qbk bytes via the shared QuickBook parser utilities and respects duplicate handling (msgctxt vs merge) when merge_duplicates is set in format params.
• save_content reconstructs .qbk output from the current store plus a template store (raises clearly if the template is missing), matching the expected Weblate convert round-trip contract.
• mimetype / extension return sensible values for QuickBook.
• boost_weblate.formats.__all__ exposes QuickBookFormat for discovery/registration.

Implementation Notes

• Keep the class thin: delegate parsing to QuickBookFile and serialization to QuickBookTranslator from boost_weblate.utils.quickbook.
• Mirror control flow and responsibilities of upstream ConvertFormat usage (see Weblate’s AsciiDocFormat / convert tests for precedent).
• Use NamedBytesIO (or equivalent) so the parser receives a file-like object with the raw template bytes.

References

• src/boost_weblate/formats/quickbook.py
• src/boost_weblate/formats/__init__.py
• Weblate: weblate.formats.convert.ConvertFormat and related convert formats
• Weblate documentation — formats / conversion