Testnet - v2.1.6

This is a Testnet and Devnet release. It is NOT recommended for Mainnet Beta.

What's Changed

• v2.1: rekey feature enable_get_epoch_stake_syscall (backport of #3627) by @mergify in #3699
• Bump version to v2.1.6 by @github-actions in #3995
• v2.1: SVM: fix executor metrics accumulation in program loader (backport of #3695) by @mergify in #3767
• v2.1: use trailing_zeros for threadset iteration (backport of #3871) by @mergify in #3897
• v2.1: fix audit (backport of #4014) by @mergify in #4022
• v2.1: Rekey direct mapping feature (backport of #4058) by @mergify in #4062
• v2.1: Update docs URL in docusaurus config (backport of #4081) by @mergify in #4087

Full Changelog: v2.1.5...v2.1.6