Allow internal types to support a `Recycler` interface, which will allow for sharing of common types across handlers.
This means that all `grid.MSS` (and similar) objects are shared across in a common pool instead of a per-handler pool.
Add internal request reuse of internal types. Add for safe (pointerless) types explicitly.
Only log params for internal types. Doing Sprint(obj) is just a bit too messy.
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