* Add missing leaf cache update when a leaf turns to a branch with two
leaves (on merge) and vice versa (on delete) - this could lead to stale
leaves being returned from the cache causing validation failures - it
didn't happen because the leaf caches were not being used efficiently :)
* Replace `seq` with `ArrayBuf` in `Hike` allowing it to become
allocation-free - this PR also works around an inefficiency in nim in
returning large types via a `var` parameter
* Use the leaf cache instead of `getVtxRc` to fetch recent leaves - this
makes the vertex cache more efficient at caching branches because fewer
leaf requests pass through it.
* pre-allocate `blobify` data and remove redundant error handling
(cannot fail on correct data)
* use threadvar for temporary storage when decoding rdb, avoiding
closure env
* speed up database walkers by avoiding many temporaries
~5% perf improvement on block import, 100x on database iteration (useful
for building analysis tooling)
hike allocations (and the garbage collection maintenance that follows)
are responsible for some 10% of cpu time (not wall time!) at this point
- this PR avoids them by stepping through the layers one step at a time,
simplifying the code at the same time.
This buffer eleminates a large part of allocations during MPT traversal,
reducing overall memory usage and GC pressure.
Ideally, we would use it throughout in the API instead of
`openArray[byte]` since the built-in length limit appropriately exposes
the natural 64-nibble depth constraint that `openArray` fails to
capture.
