* Verify headers and blocks only when needed
Curretnly we have some lightweigt validation implemented as part of
entity deserialization, which is safer and allows us to not parse the
entire object if some part is invalid. At the same time this logic
always applies when we read an entity, eg when reading from DB.
This PR introduces UntrustedHeader/Block which is used when we read from
the network. It does partial validation during read, then it is supposed
to be converted into regular header/block which doesn't validate itself.
Also this PR adds "lightweight" validation to block header read like we have
for block body, so we don't parse block body if the header is invalid.
Fixes#1642
* Move version validation to untrusted header
* update fuzz tests
* PoW context is now properly picked depending on the chain type,
edge bits and block height. Height const for T4 hard fork leaving
a couple weeks to have miners in place. Removed now unused Cuckoo context.
* Simplified block siphash
* Fix servers crate compilation
* Tiny bit cleaner block siphash. Maybe.
* Cuckatoo min edge bits update for T4 and mainnet
* Fix header size tests, Cuckatoo31 default means one more bit per edge
* Remove redundant param from verify_size
* cuck placeholder
* rustfmt
* cuckatoo, early days
* rustfmt
* data structures are in place, siphash key creation is consistent with @tromp
* solver in place, (not yet working)
* cuckatoo test solver working with test nonce
* rustfmt
* update solver to remove adjacency list removals
* verifier functioning
* rustfmt
* Proper error handing in Cuckatoo module, couple of tests
* modify cuckoo/cuckatoo solvers and verifiers to function identically, in advance of trait refactoring
* rustfmt
* refactor PoW context into trait, default to using cuckoo context
* rustfmt
* create macros for integer casting/unwraps
* don't instantiate structs when just verifying, add test validation vector for cuckatoo 29
* rustfmt
* don't init cuckoo structs if just validating
* test fix
* ensure BH hashing for POW is only done within miner/validators
