perf(cubesql): Avoid allocations in MetaContext methods #3632

Job	Run time
latest-tag-sha	19s
Build native Linux 20 x86_64-unknown-linux-gnu Python fallback	7m 42s
build	7m 1s
tests (20.x, athena-export-bucket-s3)	18m 57s
tests (20.x, bigquery-export-bucket-gcs)	8m 54s
tests (20.x, clickhouse)	5m 44s
tests (20.x, clickhouse-export-bucket-s3)	5m 32s
tests (20.x, databricks-jdbc)	6m 3s
tests (20.x, databricks-jdbc-export-bucket-s3)	6m 26s
tests (20.x, databricks-jdbc-export-bucket-azure)	6m 21s
tests (20.x, mssql)	5m 42s
tests (20.x, mysql)	5m 9s
tests (20.x, postgres)	5m 6s
tests (20.x, redshift)	5m 45s
tests (20.x, redshift-export-bucket-s3)	5m 55s
tests (20.x, snowflake)	5m 43s
tests (20.x, snowflake-export-bucket-s3)	6m 1s
tests (20.x, snowflake-export-bucket-azure)	5m 39s
tests (20.x, snowflake-export-bucket-azure-via-storage-integration)	5m 42s
tests (20.x, snowflake-export-bucket-gcs)	5m 41s
	2h 9m 22s

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