drop dependencies from dmap.js

ethers
- ethers.utils.defaultAbiCoder
- + we only need to encode one call, get
- ethers.utils.keccak256
- + find a standalone implementation
- ethers.utils.hexZeroPad
- + just extract this function
- ethers.BigNumber.from
- + use native BigInteger
- ethers.utils.Interface
- + pretty sure lib.slot is deprecated now?

ebnf
- the parser for dpath should be trivial

Start with dmap.js and trace each listed ethers dependency, then inspect how the dpath parser is currently handled. Done means the listed dependencies and parser work are addressed without changing the registry's behavior; the issue names no tests or verification command.

Written by the indexing model from the issue text.