perf(cubesql): Avoid allocations in MetaContext methods #3612

Job	Run time
Build native Linux 20 x86_64-unknown-linux-gnu Python fallback	8m 57s
latest-tag-sha	19s
build	7m 16s
tests (20.x, athena-export-bucket-s3)	18m 38s
tests (20.x, bigquery-export-bucket-gcs)	8m 48s
tests (20.x, clickhouse)	5m 47s
tests (20.x, clickhouse-export-bucket-s3)	5m 26s
tests (20.x, databricks-jdbc)	6m 42s
tests (20.x, databricks-jdbc-export-bucket-s3)	7m 22s
tests (20.x, databricks-jdbc-export-bucket-azure)	6m 48s
tests (20.x, mssql)	5m 58s
tests (20.x, mysql)	5m 52s
tests (20.x, postgres)	5m 41s
tests (20.x, redshift)	5m 33s
tests (20.x, redshift-export-bucket-s3)	5m 50s
tests (20.x, snowflake)	5m 52s
tests (20.x, snowflake-export-bucket-s3)	6m 4s
tests (20.x, snowflake-export-bucket-azure)	5m 40s
tests (20.x, snowflake-export-bucket-azure-via-storage-integration)	5m 36s
tests (20.x, snowflake-export-bucket-gcs)	5m 31s
	2h 13m 40s

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