Features

• Improve contract module serialization/deserialization speed by 30% (#4448)
• Fix some receipts that were stuck previously due to #4228 (#4248)
• Make AccountId strictly typed and correct by construction (#4621)

Fixes

• Fix neard shutdown issue (#4429, #4442)
• Address test dependency issue #4556 (#4606, #4622)

CODE_COLOR: CODE_YELLOW_TESTNET
RELEASE_VERSION: 1.21.0-rc.1
PROTOCOL_UPGRADE: TRUE
DATABASE_UPGRADE: TRUE
SECURITY_UPGRADE: FALSE