* Extract RocksDB timing tests from snap unit tests as separate module
why:
Declutter, make space for more snap related unit tests.
* Renamed `undumpNextGroup()` => `undumpBlocks()`
why:
Source file name is called `undump_blocks.nim` which should be sort
of in sync with the method name(s).
* Implement snap/1 server method `getByteCodes()`
* Implement snap/1 client method `getByteCodes()`
* Implement faculty for handling contract code fetching via snap/1
* Provide persistent storage for contract code records
* Implement contract code snap sync fetch & store
* Code massage, cosmetics
* Unit tests for verifying snap sync snapshot dump
details:
Use `undump_kvp.dumpAllDb()` to dump any database.
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