* dep: upgrade secp256k1 to use btcec/v2 v2.3.2 and update insecurity pkg
* build ci: upgrade go to 1.19 and golangci-lint to 1.50.1
* docs: fix format that does not follow the goimports
* dep: redirect github.com/bnb-chain/tendermint to v0.31.13
* ci: disable GOPROXY
This PR adds re-written difficulty calculators, which are based on uint256. It also adds a fuzzer + oss-fuzz integration for the new fuzzer. It does differential fuzzing between the new and old calculators.
Note: this PR does not actually enable the new calculators.