issue #3: add persistent classes #9

Job	Run time
ci / check if job needs to run	2s
ci / prepare test matrix	14s
ci / MOODLE_401_STABLE - mariadb - php 7.4 - tool_dynamic_cohorts	1m 20s
ci / MOODLE_401_STABLE - pgsql - php 7.4 - tool_dynamic_cohorts	1m 26s
ci / MOODLE_401_STABLE - pgsql - php 8.0 - tool_dynamic_cohorts	1m 30s
ci / MOODLE_401_STABLE - mariadb - php 8.0 - tool_dynamic_cohorts	1m 39s
ci / MOODLE_402_STABLE - pgsql - php 8.0 - tool_dynamic_cohorts	1m 31s
ci / MOODLE_402_STABLE - mariadb - php 8.1 - tool_dynamic_cohorts	1m 36s
ci / MOODLE_402_STABLE - pgsql - php 8.1 - tool_dynamic_cohorts	1m 38s
ci / MOODLE_402_STABLE - mariadb - php 8.0 - tool_dynamic_cohorts	1m 46s
ci / MOODLE_403_STABLE - pgsql - php 8.0 - tool_dynamic_cohorts	1m 29s
ci / MOODLE_403_STABLE - mariadb - php 8.0 - tool_dynamic_cohorts	1m 45s
ci / MOODLE_403_STABLE - pgsql - php 8.2 - tool_dynamic_cohorts	1m 52s
ci / MOODLE_403_STABLE - mariadb - php 8.2 - tool_dynamic_cohorts	1m 40s
ci / Release to the Moodle plugin directory	0s
	19m 28s

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