4 tests covering the open_format_emitter:
- emitJsonFromDbc round-trips a hand-built 2-record DBC through
DBCFile::load (which auto-detects JSON via the '{' prefix) and
recovers identical record/field/value data.
- Missing input file → graceful failure (no JSON written).
- Bad DBC magic → graceful failure.
- emitOpenFormats walks a subdirectory and writes the side-file
in the right place (matches the extractor's recursive walk).
Brings ctest target count to 31.
