In this commit, we update the nonce generation to support optional
parameters defined in the latest BIP draft. These parameters are
optional, but if specified my mitigate the effect of weak randomness
when generating the nonce.
Given the protocol doesn't require signers to prove how they generate
their nonces, this update is mainly to ensure strict spec compliance,
and is effectively optional.
In this commit, we add a series of new options and methods to make it
easier to use the package in the context of a taproot output that
commits to a script root or some other value. Before this series of
changes, the API was hard to use in this context as the taproot tweak
actually includes the internal public key, which in this case is the
aggregated public key. So you actually needed to call that API w/o the
tweak, get that, then recompute the tweak itself.
To make things easier in the taproot context, we've added a series of
new options that'll return the aggregated key before any tweaks (to be
used as the internal key), and also handle computing the BIP 341 tweak
value for the caller.
In this commit, we create a new package to house the ECDSA-specific
logic in the new `btcec/v2` pacakge. Thsi c hange is meant to mirror the
structure of the `dcrec` package, as we'll soon slot in our own custom
BIP-340 implementation.
In this commit, we turn the package into a new Go module (version 2),
and then port over the current set of types and functions to mainly
alias to the more optimized and maintained dcrec variant.
Taking a look at the benchmarks, most operations other than
normalization (which IIRC is a bit slower now due to constant time
fixes) enjoy some nice speeds up:
```
benchcmp is deprecated in favor of benchstat: https://pkg.go.dev/golang.org/x/perf/cmd/benchstat
benchmark old ns/op new ns/op delta
BenchmarkAddJacobian-8 464 328 -29.20%
BenchmarkAddJacobianNotZOne-8 1138 372 -67.27%
BenchmarkScalarBaseMult-8 47336 31531 -33.39%
BenchmarkScalarBaseMultLarge-8 42465 32057 -24.51%
BenchmarkScalarMult-8 123355 117579 -4.68%
BenchmarkNAF-8 582 168 -71.12%
BenchmarkSigVerify-8 175414 120794 -31.14%
BenchmarkFieldNormalize-8 23.8 24.4 +2.39%
BenchmarkParseCompressedPubKey-8 24282 10907 -55.08%
```
