move explain parser to protected status (#2099) #407

Job	Run time
db-motherduck / test-motherduck	3m 57s
db-bigquery / test-bigquery	6m 6s
db-postgres / test-postgres	4m 12s
db-snowflake / test-snowflake	6m 30s
main / main	6m 51s
npm-prerelease	4m 17s
	31m 53s

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