Turns out, it's almost always allocating because we're mostly dealing with
small integers while the buffer size is calculated in 8-byte chunks here, so
preallocated buffer is always insufficient.
name old time/op new time/op delta
ToPreallocatedBytes-8 28.5ns ± 7% 19.7ns ± 5% -30.72% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
ToPreallocatedBytes-8 16.0B ± 0% 0.0B -100.00% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
ToPreallocatedBytes-8 1.00 ± 0% 0.00 -100.00% (p=0.000 n=10+10)
Fix StorageItem reuse at the same time. We don't copy when getting values from
the storage, but we don when we're putting them, so buffer reuse could corrupt
old values.
They never return errors, so their interface should reflect that. This allows
to remove quite a lot of useless and never tested code.
Notice that Get still does return an error. It can be made not to do that, but
usually we need to differentiate between successful/unsuccessful accesses
anyway, so this doesn't help much.
We have a lot of native contract types that are converted to stack items
before serialization, then deserialized as stack items and converted back to
regular structures. stackitem.Convertible allows to remove a lot of repetitive
io.Serializable code.
This also introduces to/from converter in testserdes which unfortunately
required to change util tests to avoid circular references.
