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Chunk scan performance during querying is improved by avoiding repeated open and close of relations and indexes when joining chunk information from different metadata tables. When executing a query on a hypertable, it is expanded to include all its children chunks. However, during the expansion, the chunks that don't match the query constraints should also be excluded. The following changes are made to make the scanning and exclusion more efficient: * Ensure metadata relations and indexes are only opened once even though metadata for multiple chunks are scanned. This avoids doing repeated open and close of tables and indexes for each chunk scanned. * Avoid interleaving scans of different relations, ensuring better data locality, and having, e.g., indexes warm in cache. * Avoid unnecessary scans that repeat work already done. * Ensure chunks are locked in a consistent order (based on Oid). To enable the above changes, some refactoring was necessary. The chunk scans that happen during constraint exclusion are moved into separate source files (`chunk_scan.c`) for better structure and readability. Some test outputs are affected due to the new ordering of chunks in append relations.