Although the current hard-coder ThreadLocal-based buffer recycling (via BufferRecycler containers accessed via BufferRecyclers) has worked reasonably well up until recently, changes to later JVMs have made ThreadLocal access less beneficial; and in near future (Project Loom et al) even counter-productive.
But there are other ways to allow beneficial buffer recycling: especially for use cases where pooling is integrated with other frameworks.

To allow new default and alternative recycling schemes, let's add RecyclerPool extension point, make current implementation work with it.
And for bonus points, possibly implement one or more alternate implementations to use.