v3.21.0

Optimization v3.21.0

Diff since v3.20.2

Merged pull requests:

• Pass state to OptimizationOptimisers callback (#649) (@Vaibhavdixit02)
• downgrade CI (#650) (@ArnoStrouwen)
• CompatHelper: bump compat for LoggingExtras to 1, (keep existing compat) (#651) (@github-actions[bot])
• [WIP]Stats and State (#652) (@Vaibhavdixit02)

Closed issues:

• NonConvex package manager (#350)
• What is PolyOpt()? (#375)
• Learning rate decay in callback function (#648)